diff --git a/CONTEXT.md b/CONTEXT.md
index fe6493ee4..19825e15a 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -101,6 +101,10 @@ _Avoid_: energy assessment, site survey, field survey, Domna survey, Hestia surv
 Property data supplied by a landlord that may correct or supplement the public EPC for a single Property; triggers Rebaselining when applied; not applicable when Site Notes are present.
 _Avoid_: patches (deprecated), corrections, manual EPC, edits
 
+**Landlord-Description Classification**:
+Resolving a **Landlord Description** (unbounded free-text a landlord supplies for one component — "CWI" / "Cav filled" / "cavity insulated" all name one thing) onto a **Recognised Internal Description** via an LLM classifier, persisted in the `landlord_*_overrides` table (`source=classifier`) as a reviewed cache. Four vocabularies are kept **distinct** and must not be conflated: a **Landlord Description** (unbounded input); a **Recognised Internal Description** (the closed target taxonomy — e.g. a `MainHeatingSystemType` archetype — each binding to a Simulation Overlay); a **Lodged Description** (the gov-EPC `main_heating[].description` rendering, e.g. "Room heaters, electric" — only an example of which system *types* occur, never a map key); and the **SAP main heating code** (Table 4a/4b, what the calculator consumes). The classifier maps Landlord → Recognised Internal → SAP code. When it cannot confidently place the text it emits **`None`** (no overlay → the lodged EPC stands, surfaced to the user as "no suitable match"), **never the nearest wrong archetype** — the target taxonomy must be complete enough that a real system always has a correct home, so the classifier never overflows into a garbage-drawer archetype (ADR-0041).
+_Avoid_: "the LLM mapper is unreliable" (the failure mode is a too-small target taxonomy, not LLM language ability); conflating the landlord input vocabulary with the gov-EPC lodged rendering or the RdSAP entry-tool catalogue; treating a deterministic dict as a *replacement* for the LLM rather than a reviewed cache of its output
+
 ### Modelling
 
 **Effective EPC**:
diff --git a/applications/modelling_e2e/handler.py b/applications/modelling_e2e/handler.py
index 916c2c247..b4848f694 100644
--- a/applications/modelling_e2e/handler.py
+++ b/applications/modelling_e2e/handler.py
@@ -108,7 +108,10 @@ from repositories.product.composite_product_repository import (
 from repositories.property.in_memory_property_overrides_reader import (
     InMemoryPropertyOverridesReader,
 )
-from repositories.property.landlord_override_overlays import overlays_from
+from repositories.property.landlord_override_overlays import (
+    flag_fuel_mismatch,
+    overlays_from,
+)
 from repositories.property.override_backed_prediction_attributes_reader import (
     OverrideBackedPredictionAttributesReader,
 )
@@ -561,7 +564,9 @@ def handler(
                 epc = (
                     None  # no stored lodged EPC; prediction path handles this property
                 )
-            overrides = overlays_from(overrides_reader.overrides_for(pid))
+            resolved_overrides = overrides_reader.overrides_for(pid)
+            flag_fuel_mismatch(resolved_overrides)
+            overrides = overlays_from(resolved_overrides)
             predicted_epc: Optional[EpcPropertyData] = None
             predicted_epc_is_new = False
 
diff --git a/docs/adr/0041-landlord-heating-classification-targets-a-complete-modellable-taxonomy.md b/docs/adr/0041-landlord-heating-classification-targets-a-complete-modellable-taxonomy.md
new file mode 100644
index 000000000..47614fe56
--- /dev/null
+++ b/docs/adr/0041-landlord-heating-classification-targets-a-complete-modellable-taxonomy.md
@@ -0,0 +1,129 @@
+# Landlord-heating classification targets a complete, modellable taxonomy; unmapped input is no-override
+
+## Status
+
+accepted
+
+## Context
+
+Landlord supplementary data describes a dwelling's components in **unbounded
+free-text** — a wall is "cavity insulated" / "CWI" / "Cav filled"; a heating
+system is "communal gas boiler" / "Quantum storage" / a boiler make. An LLM
+classifier maps that free-text onto a **closed internal taxonomy** of recognised
+descriptions, each of which binds to a Simulation Overlay applied to
+`EpcPropertyData` (ADR-0032). For heating the taxonomy is the
+`MainHeatingSystemType` enum, mapped to a representative SAP Table 4a/4b code by
+`main_heating_system_overlay`, with coherent companions dragged from the code
+(ADR-0035). The LLM is the right tool for the unbounded-free-text problem; the
+deterministic dicts in legacy `asset_list` were a *reviewed cache of LLM output*,
+not a replacement, and the `landlord_*_overrides` table already serves as that
+verified cache (keyed `portfolio_id + description`).
+
+The taxonomy was **too small** — 9 heating archetypes against a ~13-family RdSAP
+main-heating taxonomy. With no correct target the classifier force-picked the
+nearest wrong archetype, and treated **"Gas CPSU" as a garbage drawer**: oil and
+solid-fuel room heaters, community heating, and `"boiler: a rated na"` all
+classified to Gas CPSU; the word "convector" in `"electric (direct acting) room
+heaters: panel, convector or radiant heaters"` pulled it to `"Electric storage
+heaters, convector"` (code 403, off-peak storage) instead of `"Electric room
+heaters"` (691, direct-acting, single-rate).
+
+Folded into the Effective EPC, a single-rate dwelling modelled as off-peak
+storage scores **SAP ~10 (band G)**. This is the true cause of **PRD #1361
+Class A** — 14 properties lodged in band C/D rebaselining to band G — which had
+been mis-attributed to a fabric "no insulation (assumed)" assumption and the
+pre-SAP10 rebaseline. The walls are correct (landlord asserted as-built); the
+heating is the crater. Exemplar **property 718066**: lodged SAP 57, landlord
+described "electric (direct acting) room heaters: panel, convector or radiant"
+(correct code 691, single-rate), mis-stored as code 403 → live SAP **9.9**. The
+stored override was classified `source=classifier` on 2026-06-20, **before** the
+691 "Electric room heaters" archetype existed (commit ada2bc07, 2026-06-29) — so
+it is also stale.
+
+## Decision
+
+The fix is the **target taxonomy, not the mapper**. The LLM stays.
+
+1. **The classifier targets a complete, modellable taxonomy.** Expand
+   `MainHeatingSystemType` + `_MAIN_HEATING_CODES` to cover every RdSAP
+   main-heating family the calculator can score: room heaters by fuel
+   (gas / oil / solid), warm air, **heat pumps**, and **community heating**. Each
+   maps to a representative Table 4a/4b code; coherent companions drag from the
+   code per ADR-0035, so adding an archetype is still "just add its code".
+
+2. **Unmapped free-text → `None`, never a forced archetype.** The overlay already
+   returns `None` (no overlay → the lodged EPC heating stands) for any value not
+   in `_MAIN_HEATING_CODES`; the classifier must *emit* Unknown/`None` when it
+   cannot confidently place the text, rather than the nearest wrong archetype.
+   "Gas CPSU" (or any other archetype) is never a fallback. The `None` mapping is
+   persisted and surfaced to the user as "no suitable match" for later edit. A
+   forced archetype overwrites a correct lodged cert; `None` (keep lodged) is the
+   only safe and honest behaviour.
+
+3. **Heat pumps are modellable without a PCDB index** — a "model unknown" heat
+   pump maps to a default Table 4a heat-pump code (211–224) with the table's
+   default seasonal efficiency; no `main_heating_index_number` is required.
+
+4. **Community heating is modelled via its explicit codes** — 301 (boiler
+   community) / 302 (CHP + boilers) / 304 (electric heat-pump community), which
+   the catalogue strings disambiguate ("community boilers only" / "community CHP
+   and boilers" / "community heat pump"). The calculator (Appendix C §C3.2
+   distribution loss, Table 12c DLF, Table 12 source factors) and Bill Derivation
+   (`HEAT_NETWORK` indicative rate) already support these. **Load-bearing
+   assumption:** when the landlord text does not supply them, the **DLF defaults
+   to Table 12c 1.50** and the source to a boiler — community SAP is *sensitive*
+   to the DLF (1.0 vs 1.5 is a large swing), so this default is documented here
+   and surfaced as an assumption. Coarse "communal heating" with **no named
+   source** falls to `None` rather than inventing a heat-network model.
+
+5. **Re-classify the stale `source=classifier` overrides** once the taxonomy is
+   complete, so the band-G properties pick up their correct code.
+
+## Considered Options
+
+- **Replace the LLM with a deterministic catalogue map** — rejected: landlord
+  input is unbounded free-text, not a closed vocabulary. The LLM is the right
+  front door; determinism belongs as a downstream *verified* cache (the override
+  table), built from LLM output + review, exactly as `asset_list` was.
+- **Keep the 9-member enum, tune the LLM prompt** — rejected: with no correct
+  target the LLM must pick a wrong archetype regardless of prompt. Target
+  completeness is the fix; prompt quality is secondary.
+- **Force unmapped input to a conservative archetype** (e.g. direct-acting
+  electric) — rejected: any forced archetype overwrites a correct lodged cert.
+- **Defer community heating to `None`** (grill option b) — rejected in favour of
+  modelling the three explicit community codes, since calculator + bill already
+  support heat networks and the catalogue strings disambiguate the cases; only
+  coarse unnamed "communal heating" falls to `None`.
+
+This extends [ADR-0032](0032-landlord-override-epc-overlay.md) (the override
+overlay) and [ADR-0035](0035-coherent-heating-system-synthesis.md) (coherent
+companions drag from the code). The visible baseline shift it produces is
+correct Rebaselining per [ADR-0039](0039-override-aware-rebaselining.md). It
+**corrects the stated cause of PRD #1361 Class A** (classifier taxonomy gap, not
+fabric/rebaseline).
+
+### Amendment: natural-fuel coherence
+
+A room-heater / direct-acting archetype names a *system*, not its fuel — and fuel
+arrives as its own composable `main_fuel` override. Two rules keep the system
+self-coherent without coupling the two overlays:
+
+- **Every archetype drags a natural fuel so the system self-coheres without a
+  `main_fuel` override.** Where the fuel is unambiguous it is exact — electric
+  room heaters / direct-acting / storage → electricity (RdSAP `main_fuel` 29), a
+  gas boiler → mains gas (26), an oil room heater → oil (28). **Solid fuel is
+  ambiguous** (coal / anthracite / smokeless / dual fuel / wood logs / pellets),
+  so it **defaults to house coal (33)** — the most common solid fuel — which a
+  specific `main_fuel` override then refines. (The `main_fuel` override's own
+  vocabulary must grow to carry the full solid-fuel list — a parallel taxonomy
+  gap, same shape as this one.)
+- **A present `main_fuel` override wins** by the applicator's last-wins
+  composition (`apply_simulations` setattrs non-`None` fields in order), so the
+  `main_fuel` overlay is applied **after** the heating overlay. The agreeing
+  case (electric system + electricity fuel) is order-immaterial; only a
+  *disagreeing* one depends on the ordering.
+- **A landlord fuel that contradicts the archetype's natural fuel is *logged*,
+  not raised** (e.g. "gas" fuel on a solid-fuel room heater) — an
+  override-plausibility signal (cf. the ADR-0039 scanner); what to do with it is
+  deferred. The override is still honoured (the landlord wins); we only record
+  the implausibility.
diff --git a/domain/epc/property_overlays/main_heating_system_overlay.py b/domain/epc/property_overlays/main_heating_system_overlay.py
index e763fea75..6069b7a49 100644
--- a/domain/epc/property_overlays/main_heating_system_overlay.py
+++ b/domain/epc/property_overlays/main_heating_system_overlay.py
@@ -68,6 +68,61 @@ _ASSUMED_DUAL_METER_CODES = OFF_PEAK_IMPLYING_HEATING_CODES | _ROOM_HEATER_CODES
 _MANUAL_CHARGE_CONTROL = 2401
 _STORAGE_HEATER_CODES = frozenset(range(401, 410))
 
+# SAP Table 4a category 10 ("Room heaters") and its conservative Table 4e Group 6
+# control. A landlord names a room heater, not its control; code 2601 ("no
+# thermostatic control of room temperature") is the lowest-SAP room-heater
+# control — the modal one real solid-fuel room-heater certs lodge — so it never
+# over-credits an unobserved control (the room-heater mirror of the storage
+# manual-charge default). Scoped per family as archetypes land; solid-fuel room
+# heaters are Table 4a 631-636.
+_ROOM_HEATER_CATEGORY = 10
+_ROOM_HEATER_CONTROL = 2601
+_SOLID_FUEL_ROOM_HEATER_CODES = frozenset(range(631, 637))
+# Oil room heaters (SAP Table 4a 621-625) — category 10, conservative room-heater
+# control, natural fuel heating oil (RdSAP main_fuel 28).
+_OIL_ROOM_HEATER_CODES = frozenset(range(621, 626))
+_OIL_FUEL = 28
+# Gas (incl. LPG) room heaters (SAP Table 4a 601-613) — category 10, conservative
+# control, natural fuel mains gas (26); an LPG dwelling is refined by a main_fuel
+# override (the overlay can't see the mains connection).
+_GAS_ROOM_HEATER_CODES = frozenset(range(601, 614))
+# Fuel-burning room heaters (solid + oil + gas) share category 10 + the
+# conservative room-heater control; only the natural fuel differs by family.
+# (Distinct from `_ROOM_HEATER_CODES` above, the electric-room-heater dual-meter
+# set.)
+_CATEGORY_10_ROOM_HEATER_CODES = (
+    _SOLID_FUEL_ROOM_HEATER_CODES | _OIL_ROOM_HEATER_CODES | _GAS_ROOM_HEATER_CODES
+)
+
+# Natural-fuel coherence (ADR-0041): where an archetype unambiguously implies a
+# fuel, the overlay drags it so a system-only override is self-coherent on a cert
+# that lodged a different fuel. A later `main_fuel` override still wins (last-wins
+# composition); a contradicting landlord fuel is logged, not silently overridden.
+# Electric room heaters (Table 4a 691-701) are unambiguously electricity (RdSAP
+# main_fuel code 29). Solid fuel is ambiguous (coal / anthracite / smokeless /
+# dual fuel / wood logs / pellets), so it defaults to house coal (33) — the most
+# common solid fuel — when the landlord gives no `main_fuel` override; a specific
+# solid-fuel override still wins by last-wins composition.
+_ELECTRICITY_FUEL = 29
+_HOUSE_COAL_FUEL = 33
+_ELECTRIC_ROOM_HEATER_CODES = frozenset(range(691, 702))
+
+# Heat pumps (SAP Table 4a 211-224 wet, 521-527 warm-air) are category 4 and
+# unambiguously electric (natural fuel 29). Modellable on the default code's SPF
+# without a PCDB index (ADR-0041).
+_HEAT_PUMP_CATEGORY = 4
+_HEAT_PUMP_CODES = frozenset(range(211, 225)) | frozenset(range(521, 528))
+
+# Community / heat-network heating (SAP Table 4a 301-304) is category 6; the
+# calculator's `_is_heat_network` keys off code OR category 6. The boiler-driven
+# schemes (301/302/303) are dominantly mains gas (community) — RdSAP main_fuel 20
+# — per real community certs; the heat-pump scheme (304) is electricity
+# (community), added with its archetype (ADR-0041).
+_HEAT_NETWORK_CATEGORY = 6
+_HEAT_NETWORK_CODES = frozenset({301, 302, 303, 304})
+_COMMUNITY_BOILER_CODES = frozenset({301, 302, 303})
+_COMMUNITY_GAS_FUEL = 20
+
 # SAP Table 4c full boiler-control code: programmer + room thermostat + TRVs. The
 # landlord names the boiler, not its controls — but a gas boiler installed under
 # modern Building Regs must carry compliant controls, and this overlay already
@@ -109,6 +164,29 @@ _MAIN_HEATING_CODES: dict[str, int] = {
     "Electric storage heaters, fan": 404,
     "Direct-acting electric": 191,
     "Electric room heaters": 691,
+    "Solid fuel room heater, closed": 633,
+    # Default air-source heat pump — SAP Table 4a 211 ("flow temp in other
+    # cases", default SPF 2.30). Modellable without a PCDB index; an actual
+    # product index would refine it (ADR-0041).
+    "Air source heat pump": 211,
+    # Boiler-driven community / heat-network heating — SAP Table 4a 301. The
+    # calculator derives the heat-source efficiency (80%) + DLF (1.50 default)
+    # from the code (cert_to_inputs). A generic "Community heating" with no named
+    # source stays unmapped (-> None) — the source can't be assumed (ADR-0041).
+    "Community heating, boilers": 301,
+    # Community CHP + boilers — SAP Table 4a 302 (heat network, category 6).
+    "Community heating, CHP and boilers": 302,
+    # Modern standalone oil room heater — SAP Table 4a 623 ("Oil room heater,
+    # 2000 or later", no boiler). Natural fuel heating oil (ADR-0041).
+    "Oil room heater, 2000 or later": 623,
+    # Gas room heaters — each catalogue variant to its own SAP Table 4a code
+    # (wide efficiency spread, so no single representative). Natural fuel mains
+    # gas; an LPG dwelling is refined by a `main_fuel` override (ADR-0041).
+    "Gas room heater, condensing fire": 611,
+    "Gas room heater, decorative fuel-effect": 612,
+    "Gas room heater, flush live-effect": 605,
+    "Gas room heater, open flue 1980 or later": 603,
+    "Gas room heater, open flue pre-1980": 601,
 }
 
 
@@ -129,6 +207,38 @@ def _control_for(code: int) -> Optional[int]:
         return _MANUAL_CHARGE_CONTROL
     if code in _GAS_BOILER_CODES:
         return _FULL_BOILER_CONTROL
+    if code in _CATEGORY_10_ROOM_HEATER_CODES:
+        return _ROOM_HEATER_CONTROL
+    return None
+
+
+def _category_for(code: int) -> Optional[int]:
+    """The SAP Table 4a heating category a code implies, where the archetype
+    fixes it. Room heaters are category 10 — set so a system-only override reads
+    as a room-heater system, not whatever category the replaced system carried."""
+    if code in _CATEGORY_10_ROOM_HEATER_CODES:
+        return _ROOM_HEATER_CATEGORY
+    if code in _HEAT_PUMP_CODES:
+        return _HEAT_PUMP_CATEGORY
+    if code in _HEAT_NETWORK_CODES:
+        return _HEAT_NETWORK_CATEGORY
+    return None
+
+
+def _natural_fuel_for(code: int) -> Optional[int]:
+    """The fuel an archetype unambiguously implies (a coherent default), or None
+    where the fuel is ambiguous and must come from the `main_fuel` override. A
+    present `main_fuel` override wins by last-wins composition."""
+    if code in _ELECTRIC_ROOM_HEATER_CODES or code in _HEAT_PUMP_CODES:
+        return _ELECTRICITY_FUEL
+    if code in _SOLID_FUEL_ROOM_HEATER_CODES:
+        return _HOUSE_COAL_FUEL
+    if code in _OIL_ROOM_HEATER_CODES:
+        return _OIL_FUEL
+    if code in _GAS_ROOM_HEATER_CODES:
+        return _MAINS_GAS_FUEL
+    if code in _COMMUNITY_BOILER_CODES:
+        return _COMMUNITY_GAS_FUEL
     return None
 
 
@@ -151,6 +261,16 @@ def _gas_boiler_overlay(code: int) -> HeatingOverlay:
     )
 
 
+def natural_fuel_for(main_heating_value: str) -> Optional[int]:
+    """The RdSAP `main_fuel` code a heating archetype unambiguously implies — its
+    natural fuel (ADR-0041) — or None for an unmapped archetype. Exposed so a
+    plausibility check can compare it against a landlord `main_fuel` override."""
+    code = _MAIN_HEATING_CODES.get(main_heating_value)
+    if code is None:
+        return None
+    return _natural_fuel_for(code)
+
+
 def main_heating_overlay_for(
     main_heating_value: str, building_part: int
 ) -> Optional[EpcSimulation]:
@@ -162,6 +282,8 @@ def main_heating_overlay_for(
     return EpcSimulation(
         heating=HeatingOverlay(
             sap_main_heating_code=code,
+            main_heating_category=_category_for(code),
+            main_fuel_type=_natural_fuel_for(code),
             meter_type=_meter_for(code),
             main_heating_control=_control_for(code),
             # A landlord override describes the existing dwelling, so its assumed
diff --git a/domain/epc/property_overrides/main_heating_system_type.py b/domain/epc/property_overrides/main_heating_system_type.py
index 3bfff01e5..d79fec1d1 100644
--- a/domain/epc/property_overrides/main_heating_system_type.py
+++ b/domain/epc/property_overrides/main_heating_system_type.py
@@ -25,4 +25,14 @@ class MainHeatingSystemType(Enum):
     ELECTRIC_STORAGE_FAN = "Electric storage heaters, fan"
     DIRECT_ELECTRIC = "Direct-acting electric"
     ELECTRIC_ROOM_HEATERS = "Electric room heaters"
+    SOLID_FUEL_ROOM_HEATER_CLOSED = "Solid fuel room heater, closed"
+    AIR_SOURCE_HEAT_PUMP = "Air source heat pump"
+    COMMUNITY_BOILERS = "Community heating, boilers"
+    COMMUNITY_CHP_AND_BOILERS = "Community heating, CHP and boilers"
+    OIL_ROOM_HEATER_POST_2000 = "Oil room heater, 2000 or later"
+    GAS_FIRE_CONDENSING = "Gas room heater, condensing fire"
+    GAS_FIRE_DECORATIVE = "Gas room heater, decorative fuel-effect"
+    GAS_FIRE_FLUSH_LIVE_EFFECT = "Gas room heater, flush live-effect"
+    GAS_FIRE_OPEN_FLUE_POST_1980 = "Gas room heater, open flue 1980 or later"
+    GAS_FIRE_OPEN_FLUE_PRE_1980 = "Gas room heater, open flue pre-1980"
     UNKNOWN = "Unknown"
diff --git a/repositories/property/landlord_override_overlays.py b/repositories/property/landlord_override_overlays.py
index b65cf5d29..29ebcea00 100644
--- a/repositories/property/landlord_override_overlays.py
+++ b/repositories/property/landlord_override_overlays.py
@@ -28,6 +28,7 @@ values are live vs no-op before any write.
 
 from __future__ import annotations
 
+import logging
 from typing import Callable, Optional
 
 from domain.epc.property_overlays.attribute_overlay import (
@@ -41,6 +42,7 @@ from domain.epc.property_overlays.glazing_overlay import glazing_overlay_for
 from domain.epc.property_overlays.main_fuel_overlay import fuel_overlay_for
 from domain.epc.property_overlays.main_heating_system_overlay import (
     main_heating_overlay_for,
+    natural_fuel_for,
 )
 from domain.epc.property_overlays.water_heating_overlay import (
     water_heating_overlay_for,
@@ -50,6 +52,8 @@ from domain.epc.property_overlays.wall_type_overlay import wall_overlay_for
 from domain.modelling.simulation import EpcSimulation
 from repositories.property.property_overrides_reader import ResolvedPropertyOverrides
 
+logger = logging.getLogger(__name__)
+
 # Each override component maps its value (+ building part) to an overlay, or None
 # when the value isn't resolvable. Fabric (wall/roof) folds onto building parts;
 # property_type / built_form_type are whole-dwelling categorical corrections
@@ -67,9 +71,22 @@ _COMPONENT_OVERLAYS: dict[str, Callable[[str, int], Optional[EpcSimulation]]] =
 }
 
 
+# Components whose overlay must be applied LAST so an explicit value wins a
+# default another overlay dragged. `apply_simulations` is last-wins and override
+# rows arrive in arbitrary order, so a `main_fuel` override must be applied after
+# the `main_heating_system` archetype, whose natural-fuel default it overrides
+# (ADR-0041) — e.g. "smokeless coal" must beat a solid-fuel room heater's coal
+# default.
+_APPLY_LAST: frozenset[str] = frozenset({"main_fuel"})
+
+
 def overlays_from(overrides: ResolvedPropertyOverrides) -> list[EpcSimulation]:
     overlays: list[EpcSimulation] = []
-    for row in overrides.rows:
+    # Stable sort: non-`_APPLY_LAST` rows keep their order, `main_fuel` goes last.
+    ordered_rows = sorted(
+        overrides.rows, key=lambda row: row.override_component in _APPLY_LAST
+    )
+    for row in ordered_rows:
         mapper = _COMPONENT_OVERLAYS.get(row.override_component)
         if mapper is None:
             continue
@@ -77,3 +94,55 @@ def overlays_from(overrides: ResolvedPropertyOverrides) -> list[EpcSimulation]:
         if overlay is not None:
             overlays.append(overlay)
     return overlays
+
+
+# Coarse fuel family per RdSAP `main_fuel` code (main_fuel_overlay._FUEL_CODES),
+# for the plausibility check. The natural fuel a solid-fuel archetype drags
+# (house coal) is a *default* across the ambiguous solid family, so a same-family
+# override (smokeless / dual fuel / biomass) is a refinement, not a contradiction
+# — only a different family (gas/electric on a solid heater) is flagged.
+_FUEL_FAMILY: dict[int, str] = {
+    26: "gas", 20: "gas",
+    27: "lpg", 3: "lpg", 17: "lpg",
+    28: "oil",
+    29: "electricity", 25: "electricity",
+    33: "solid", 15: "solid", 10: "solid", 31: "solid",
+}
+
+
+def _override_value(overrides: ResolvedPropertyOverrides, component: str) -> Optional[str]:
+    for row in overrides.rows:
+        if row.override_component == component:
+            return row.override_value
+    return None
+
+
+def flag_fuel_mismatch(overrides: ResolvedPropertyOverrides) -> None:
+    """Log (not raise) when a landlord `main_fuel` override contradicts the
+    `main_heating_system` archetype's natural fuel — a plausibility signal (e.g.
+    a gas fuel on an electric room heater). The override is still honoured (it
+    wins, ADR-0041); we only record the implausibility. Deferred handling."""
+    heating_value = _override_value(overrides, "main_heating_system")
+    fuel_value = _override_value(overrides, "main_fuel")
+    if heating_value is None or fuel_value is None:
+        return
+    natural = natural_fuel_for(heating_value)
+    fuel_overlay = fuel_overlay_for(fuel_value, 0)
+    override_fuel = (
+        fuel_overlay.heating.main_fuel_type
+        if fuel_overlay is not None and fuel_overlay.heating is not None
+        else None
+    )
+    if natural is None or not isinstance(override_fuel, int):
+        return
+    natural_family = _FUEL_FAMILY.get(natural)
+    override_family = _FUEL_FAMILY.get(override_fuel)
+    if natural_family is None or override_family is None:
+        return
+    if natural_family != override_family:
+        logger.warning(
+            "Landlord main_fuel %r contradicts the natural fuel of heating "
+            "system %r (override is honoured; flagged for review)",
+            fuel_value,
+            heating_value,
+        )
diff --git a/repositories/property/property_postgres_repository.py b/repositories/property/property_postgres_repository.py
index dec92814e..1072c18d8 100644
--- a/repositories/property/property_postgres_repository.py
+++ b/repositories/property/property_postgres_repository.py
@@ -14,7 +14,10 @@ from domain.property.properties import Properties
 from domain.property.property import Property, PropertyIdentity
 from infrastructure.postgres.property_table import PropertyRow
 from repositories.epc.epc_repository import EpcRepository
-from repositories.property.landlord_override_overlays import overlays_from
+from repositories.property.landlord_override_overlays import (
+    flag_fuel_mismatch,
+    overlays_from,
+)
 from repositories.property.property_overrides_reader import PropertyOverridesReader
 from repositories.property.property_repository import (
     PropertyIdentityInsert,
@@ -63,7 +66,9 @@ class PropertyPostgresRepository(PropertyRepository):
         no reader is wired (the overlay stays off) or the Property has none."""
         if self._overrides_reader is None:
             return []
-        return overlays_from(self._overrides_reader.overrides_for(property_id))
+        overrides = self._overrides_reader.overrides_for(property_id)
+        flag_fuel_mismatch(overrides)
+        return overlays_from(overrides)
 
     def get(self, property_id: int) -> Property:
         row = self._session.get(PropertyRow, property_id)
diff --git a/scripts/reclassify_heating_overrides.py b/scripts/reclassify_heating_overrides.py
new file mode 100644
index 000000000..002ebef9b
--- /dev/null
+++ b/scripts/reclassify_heating_overrides.py
@@ -0,0 +1,176 @@
+"""One-time re-classification of stale landlord main-heating-system overrides.
+
+PRD #1361 Class A: the LLM landlord-description classifier ran against a
+too-small `MainHeatingSystemType` taxonomy (ADR-0041), so canonical RdSAP
+heating descriptions were stored against the wrong archetype — community heating
+and oil/solid room heaters dumped into "Gas CPSU", and direct-acting
+"panel, convector or radiant" room heaters mis-read as off-peak storage (the
+band-G crater). The taxonomy is now complete, so these *canonical* descriptions
+re-resolve deterministically — no LLM, no nondeterminism.
+
+This rewrites the resolved archetype on every affected row in BOTH the
+per-Property fact layer (`property_overrides.override_value`) and the
+per-portfolio classifier cache (`landlord_main_heating_system_overrides.value`),
+keyed on the raw description (`original_spreadsheet_description` / `description`).
+
+DRY-RUN BY DEFAULT: prints the row counts it would change and writes nothing.
+Pass `--apply` to execute inside a transaction. Idempotent — only rows whose
+stored value differs from the corrected archetype are touched, so a second run
+is a no-op. Descriptions with no confident archetype yet (solid-fuel open-fire /
+with-boiler, warm air, electric underfloor) are deliberately NOT remapped here.
+"""
+
+from __future__ import annotations
+
+import argparse
+
+from sqlalchemy import text
+
+from domain.epc.property_overrides.main_heating_system_type import (
+    MainHeatingSystemType,
+)
+from scripts.e2e_common import build_engine, load_env
+
+# Canonical RdSAP main-heating description (lowercased, as stored in
+# `original_spreadsheet_description` / `description`) → the corrected archetype.
+# Only descriptions whose correct archetype now exists in the taxonomy appear
+# here; the value is a `MainHeatingSystemType` so a typo can't slip a non-archetype
+# string into the DB (the enum is the single source of truth — ADR-0041).
+REMAP: dict[str, MainHeatingSystemType] = {
+    "community heating systems: community boilers only (rdsap)": (
+        MainHeatingSystemType.COMMUNITY_BOILERS
+    ),
+    "community heating systems: community chp and boilers (rdsap)": (
+        MainHeatingSystemType.COMMUNITY_CHP_AND_BOILERS
+    ),
+    "electric (direct acting) room heaters: panel, convector or radiant heaters": (
+        MainHeatingSystemType.ELECTRIC_ROOM_HEATERS
+    ),
+    "oil room heaters: room heater, 2000 or later": (
+        MainHeatingSystemType.OIL_ROOM_HEATER_POST_2000
+    ),
+    "solid fuel room heaters: closed room heater": (
+        MainHeatingSystemType.SOLID_FUEL_ROOM_HEATER_CLOSED
+    ),
+    "gas (including lpg) room heaters: condensing gas fire": (
+        MainHeatingSystemType.GAS_FIRE_CONDENSING
+    ),
+    "gas (including lpg) room heaters: decorative fuel effect gas fire, "
+    "open to chimney": MainHeatingSystemType.GAS_FIRE_DECORATIVE,
+    "gas (including lpg) room heaters: flush fitting live fuel effect gas fire "
+    "(open fronted), sealed to fireplace opening": (
+        MainHeatingSystemType.GAS_FIRE_FLUSH_LIVE_EFFECT
+    ),
+    "gas (including lpg) room heaters: gas fire, open flue, 1980 or later "
+    "(open fronted), sitting proud of, and sealed to, fireplace opening": (
+        MainHeatingSystemType.GAS_FIRE_OPEN_FLUE_POST_1980
+    ),
+    "gas (including lpg) room heaters: gas fire, open flue, pre-1980 "
+    "(open fronted)": MainHeatingSystemType.GAS_FIRE_OPEN_FLUE_PRE_1980,
+}
+
+# property_overrides keys the raw text on `original_spreadsheet_description`; the
+# classifier cache keys it on `description`. Both compared case-insensitively.
+_PROPERTY_OVERRIDES_UPDATE = text(
+    """
+    UPDATE property_overrides
+       SET override_value = :new_value
+     WHERE override_component = 'main_heating_system'
+       AND lower(original_spreadsheet_description) = :description
+       AND override_value <> :new_value
+    """
+)
+# The cache `value` column is the Drizzle-owned `main_heating_system` pgEnum;
+# compare/update it as text (no CAST) so a target value the DB enum does not yet
+# carry doesn't error the read. The UPDATE is only issued for values the live
+# enum already has — `_db_enum_values` gates it (see main()).
+_CACHE_UPDATE = text(
+    """
+    UPDATE landlord_main_heating_system_overrides
+       SET value = :new_value, updated_at = now()
+     WHERE lower(description) = :description
+       AND value::text <> :new_value
+    """
+)
+_PROPERTY_OVERRIDES_COUNT = text(
+    """
+    SELECT count(*) FROM property_overrides
+     WHERE override_component = 'main_heating_system'
+       AND lower(original_spreadsheet_description) = :description
+       AND override_value <> :new_value
+    """
+)
+_CACHE_COUNT = text(
+    """
+    SELECT count(*) FROM landlord_main_heating_system_overrides
+     WHERE lower(description) = :description
+       AND value::text <> :new_value
+    """
+)
+_ENUM_VALUES = text(
+    "SELECT e.enumlabel FROM pg_enum e JOIN pg_type t ON t.oid = e.enumtypid "
+    "WHERE t.typname = 'main_heating_system'"
+)
+
+
+def main() -> None:
+    load_env()
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--apply",
+        action="store_true",
+        help="execute the updates (default: dry-run, writes nothing)",
+    )
+    args = parser.parse_args()
+
+    engine = build_engine()
+    with engine.begin() as conn:
+        conn.execute(text("SET statement_timeout = 120000"))
+        # The cache `value` is the Drizzle-owned pgEnum; only update it for
+        # archetypes the live enum already carries. The rest need the Drizzle
+        # migration (FE repo) before the cache — and the classifier — can store
+        # them; property_overrides (TEXT, what the modelling reads) is updated
+        # regardless, which is the actual band-G fix.
+        enum_values = {r[0] for r in conn.execute(_ENUM_VALUES)}
+        prop_total = 0
+        cache_total = 0
+        deferred: list[str] = []
+        for description, archetype in REMAP.items():
+            params = {"description": description, "new_value": archetype.value}
+            prop_n = conn.execute(_PROPERTY_OVERRIDES_COUNT, params).scalar() or 0
+            prop_total += prop_n
+            in_enum = archetype.value in enum_values
+            cache_n = conn.execute(_CACHE_COUNT, params).scalar() or 0 if in_enum else 0
+            cache_total += cache_n
+            if not in_enum and prop_n:
+                deferred.append(archetype.value)
+            if prop_n or cache_n:
+                tag = "" if in_enum else "  [cache deferred: enum value missing]"
+                print(
+                    f"  {prop_n:>6} property_overrides + {cache_n} cache "
+                    f"-> {archetype.value!r}  <= {description!r}{tag}"
+                )
+            if args.apply:
+                conn.execute(_PROPERTY_OVERRIDES_UPDATE, params)
+                if in_enum:
+                    conn.execute(_CACHE_UPDATE, params)
+        verb = "updated" if args.apply else "would update"
+        print(
+            f"\n{verb} {prop_total} property_overrides rows + {cache_total} "
+            f"classifier-cache rows across {len(REMAP)} descriptions."
+        )
+        if deferred:
+            print(
+                f"\n{len(set(deferred))} archetype(s) NOT in the Drizzle "
+                "`main_heating_system` pgEnum — their cache rows are deferred "
+                "until the FE-repo enum migration lands (property_overrides was "
+                "still updated, which is what the modelling reads):"
+            )
+            for v in sorted(set(deferred)):
+                print(f"    {v!r}")
+        if not args.apply:
+            print("\nDRY-RUN — nothing written. Re-run with --apply to execute.")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index ea73c0f70..d98d01458 100644
--- a/tests/domain/epc/test_main_heating_system_overlay.py
+++ b/tests/domain/epc/test_main_heating_system_overlay.py
@@ -245,13 +245,14 @@ def test_off_peak_archetypes_drag_dual_others_drag_single() -> None:
 
 @pytest.mark.parametrize(
     "main_heating_value",
-    ["Unknown", "", "Air source heat pump", "Community heating"],
+    ["Unknown", "", "Community heating"],
 )
 def test_unresolvable_or_unmodelled_heating_produces_no_overlay(
     main_heating_value: str,
 ) -> None:
-    # Heat pumps (main_heating_index_number) and community heating (community
-    # codes) don't map to a Table 4b sap_main_heating_code yet — no overlay.
+    # Genuinely unrecognised values (Unknown / empty) and not-yet-modelled
+    # community heating produce no overlay — the lodged EPC heating stands
+    # (ADR-0041). Air source heat pumps ARE now modelled (Table 4a 211).
 
     # Act
     simulation = main_heating_overlay_for(main_heating_value, 0)
@@ -383,3 +384,238 @@ def test_every_resolvable_main_heating_value_decodes(
 
     # Assert
     assert simulation is not None
+
+
+def test_solid_fuel_room_heater_decodes_to_the_closed_room_heater_code() -> None:
+    # A landlord-named solid-fuel room heater (e.g. a closed stove) is a
+    # recognised archetype, not a gas wet system — it must decode to its SAP
+    # Table 4a code (633, closed solid-fuel room heater), not overflow into the
+    # nearest wrong archetype the way the under-populated taxonomy did, sending
+    # "solid fuel room heaters: closed room heater" to Gas CPSU (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Solid fuel room heater, closed", 0)
+
+    # Assert — SAP Table 4a code 633 (closed solid-fuel room heater).
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.sap_main_heating_code == 633
+
+
+def test_solid_fuel_room_heater_drags_its_coherent_room_heater_companions() -> None:
+    # The landlord names the system, not its category/control/meter. A solid-fuel
+    # room heater is a room-heater system (Table 4a category 10) on a single-rate
+    # meter (not off-peak storage), under the conservative room-heater control
+    # real certs lodge (Table 4e Group 6 code 2601 — "no thermostatic control",
+    # the lowest-SAP room-heater control, so it never over-credits an unobserved
+    # control, mirroring the storage manual-charge default). ADR-0035.
+
+    # Act
+    simulation = main_heating_overlay_for("Solid fuel room heater, closed", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    heating = simulation.heating
+    assert heating.main_heating_category == 10
+    assert heating.main_heating_control == 2601
+    assert heating.meter_type == "Single"
+
+
+def test_electric_room_heaters_drag_their_natural_electricity_fuel() -> None:
+    # A landlord names the system; an electric room heater's natural fuel is
+    # unambiguously electricity (RdSAP main_fuel code 29). The overlay drags it so
+    # a system-only override is self-coherent even on a cert that lodged a
+    # different fuel — a later `main_fuel` override still wins (last-wins
+    # composition), and a contradicting fuel is logged, not silently kept
+    # (ADR-0041 natural-fuel coherence).
+
+    # Act
+    simulation = main_heating_overlay_for("Electric room heaters", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.main_fuel_type == 29
+
+
+def test_solid_fuel_room_heater_defaults_to_house_coal_as_its_natural_fuel() -> None:
+    # Solid fuel is fuel-ambiguous (coal / anthracite / smokeless / dual fuel /
+    # wood logs / pellets), but the system must still self-cohere when no
+    # main_fuel override is given. Default to house coal (RdSAP main_fuel code
+    # 33), the most common solid fuel; a main_fuel override naming a specific
+    # solid fuel still wins by last-wins composition (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Solid fuel room heater, closed", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.main_fuel_type == 33
+
+
+def test_air_source_heat_pump_decodes_to_the_default_ashp_code() -> None:
+    # A landlord names "air source heat pump" without a PCDB model. It is
+    # modellable via the SAP Table 4a default ASHP code (211, "flow temp in other
+    # cases", default SPF 2.30) — no main_heating_index_number needed — so it must
+    # decode to 211, not produce no overlay / fall to Unknown (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Air source heat pump", 0)
+
+    # Assert — SAP Table 4a code 211 (default air-source heat pump).
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.sap_main_heating_code == 211
+
+
+def test_air_source_heat_pump_drags_its_coherent_companions() -> None:
+    # A heat pump is unambiguously electric (natural fuel 29) and SAP Table 4a
+    # category 4. Unlike storage/CPSU it does NOT imply an off-peak tariff (SAP
+    # §12 Rule 3 is conditional, not forcing), so the coherent default meter is
+    # single-rate — forcing Dual would assume an off-peak split it may not have
+    # and mis-bill it. The overlay drags these code-derived companions so a
+    # system-only override is self-coherent (ADR-0035 / ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Air source heat pump", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    heating = simulation.heating
+    assert heating.main_heating_category == 4
+    assert heating.main_fuel_type == 29
+    assert heating.meter_type == "Single"
+
+
+def test_community_boilers_decode_to_the_heat_network_boiler_code() -> None:
+    # A community/heat-network scheme driven by boilers is SAP Table 4a code 301
+    # (the calculator derives the heat-source efficiency + DLF from it). It must
+    # decode to 301, not the Gas CPSU (120) the under-populated taxonomy forced —
+    # a single-dwelling gas wet boiler is the wrong picture for a heat network
+    # (ADR-0041). A generic "Community heating" with no named source stays None.
+
+    # Act
+    simulation = main_heating_overlay_for("Community heating, boilers", 0)
+
+    # Assert — SAP Table 4a code 301 (boiler-driven community heating).
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.sap_main_heating_code == 301
+
+
+def test_community_boilers_drag_heat_network_category_and_a_community_gas_fuel() -> None:
+    # A community boiler scheme is SAP main_heating_category 6 (heat network), so
+    # the calculator treats it as a heat network (cert_to_inputs `_is_heat_network`
+    # checks code OR category 6). Its natural fuel is mains gas (community) — RdSAP
+    # main_fuel code 20, the dominant fuel real community-boiler certs lodge. A
+    # specific main_fuel override (e.g. biomass community) still wins (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Community heating, boilers", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    heating = simulation.heating
+    assert heating.main_heating_category == 6
+    assert heating.main_fuel_type == 20
+
+
+def test_community_chp_and_boilers_decode_to_their_heat_network_code() -> None:
+    # A community scheme with CHP + boilers is SAP Table 4a code 302, still a heat
+    # network (category 6) on community mains gas (20). Real audit data: 10
+    # properties carry this, today mis-bucketed to Gas CPSU (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Community heating, CHP and boilers", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    heating = simulation.heating
+    assert heating.sap_main_heating_code == 302
+    assert heating.main_heating_category == 6
+    assert heating.main_fuel_type == 20
+
+
+def test_oil_room_heater_decodes_to_the_post_2000_code() -> None:
+    # A modern standalone oil room heater is SAP Table 4a code 623 ("Oil room
+    # heater, 2000 or later", no boiler). It must decode to 623, not the Gas CPSU
+    # the under-populated taxonomy forced (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Oil room heater, 2000 or later", 0)
+
+    # Assert — SAP Table 4a code 623.
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.sap_main_heating_code == 623
+
+
+def test_oil_room_heater_drags_its_coherent_room_heater_companions() -> None:
+    # An oil room heater is a room-heater system (category 10) on a single-rate
+    # meter, under the conservative room-heater control (2601), with its natural
+    # fuel heating oil (RdSAP main_fuel 28). The overlay drags these so a
+    # system-only override is self-coherent (ADR-0035 / ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Oil room heater, 2000 or later", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    heating = simulation.heating
+    assert heating.main_heating_category == 10
+    assert heating.main_heating_control == 2601
+    assert heating.main_fuel_type == 28
+    assert heating.meter_type == "Single"
+
+
+@pytest.mark.parametrize(
+    ("value", "code"),
+    [
+        ("Gas room heater, condensing fire", 611),
+        ("Gas room heater, decorative fuel-effect", 612),
+        ("Gas room heater, flush live-effect", 605),
+        ("Gas room heater, open flue 1980 or later", 603),
+        ("Gas room heater, open flue pre-1980", 601),
+    ],
+)
+def test_gas_room_heater_variants_decode_to_their_sap_codes(
+    value: str, code: int
+) -> None:
+    # Gas room heaters span a wide efficiency range (decorative 0.20 -> condensing
+    # 0.85), so each catalogue variant maps to its own SAP Table 4a code rather
+    # than collapsing to one representative — which would over-credit a decorative
+    # fire and under-credit a condensing one. Today they mis-bucket to "Gas
+    # boiler, regular" (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for(value, 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.sap_main_heating_code == code
+
+
+def test_gas_room_heater_drags_its_coherent_companions() -> None:
+    # A gas room heater is a room-heater system (category 10) on a single-rate
+    # meter, under the conservative room-heater control (2601). Its natural fuel
+    # is mains gas (26) — an LPG dwelling is refined by a main_fuel override
+    # (the overlay can't see the mains connection) (ADR-0041).
+
+    # Act
+    simulation = main_heating_overlay_for("Gas room heater, condensing fire", 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.heating is not None
+    heating = simulation.heating
+    assert heating.main_heating_category == 10
+    assert heating.main_heating_control == 2601
+    assert heating.main_fuel_type == 26
+    assert heating.meter_type == "Single"
diff --git a/tests/repositories/property/test_landlord_override_overlays.py b/tests/repositories/property/test_landlord_override_overlays.py
index 1f790aa88..e35034ebc 100644
--- a/tests/repositories/property/test_landlord_override_overlays.py
+++ b/tests/repositories/property/test_landlord_override_overlays.py
@@ -6,12 +6,23 @@ that fold onto the lodged EPC — per component, partial, skipping unmapped rows
 
 from __future__ import annotations
 
+import logging
+
+import pytest
+
 from datatypes.epc.domain.epc_property_data import BuildingPartIdentifier
-from repositories.property.landlord_override_overlays import overlays_from
+from domain.modelling.scoring.overlay_applicator import apply_simulations
+from repositories.property.landlord_override_overlays import (
+    flag_fuel_mismatch,
+    overlays_from,
+)
 from repositories.property.property_overrides_reader import (
     ResolvedPropertyOverride,
     ResolvedPropertyOverrides,
 )
+from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
+    build_epc,
+)
 
 
 def test_roof_type_row_produces_a_roof_overlay() -> None:
@@ -143,3 +154,74 @@ def test_unresolvable_rows_are_skipped() -> None:
 
     # Assert
     assert overlays == []
+
+
+def test_main_fuel_override_wins_over_a_heating_archetype_natural_fuel() -> None:
+    # A heating-system override drags a natural fuel (a solid-fuel room heater
+    # defaults to house coal, RdSAP main_fuel 33), but an explicit main_fuel
+    # override must win. apply_simulations is last-wins and the override rows
+    # arrive in arbitrary order, so overlays_from must apply main_fuel AFTER
+    # main_heating_system — otherwise the natural-fuel default clobbers the
+    # explicit fuel (ADR-0041). The rows here are in the order that exposes it.
+    baseline = build_epc()
+    overrides = ResolvedPropertyOverrides(
+        rows=(
+            ResolvedPropertyOverride("main_fuel", 0, "smokeless coal"),
+            ResolvedPropertyOverride(
+                "main_heating_system", 0, "Solid fuel room heater, closed"
+            ),
+        )
+    )
+
+    # Act
+    result = apply_simulations(baseline, overlays_from(overrides))
+
+    # Assert — the explicit fuel (smokeless coal 15) wins over the coal default.
+    assert result.sap_heating.main_heating_details[0].main_fuel_type == 15
+
+
+def test_a_fuel_override_contradicting_the_heating_archetype_is_logged(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    # An electric room heater is unambiguously electricity; a "mains gas" main_fuel
+    # override contradicts it (a different fuel family). The override still wins
+    # (ADR-0041), but the implausibility is logged for later review — not raised.
+    overrides = ResolvedPropertyOverrides(
+        rows=(
+            ResolvedPropertyOverride(
+                "main_heating_system", 0, "Electric room heaters"
+            ),
+            ResolvedPropertyOverride("main_fuel", 0, "mains gas"),
+        )
+    )
+
+    # Act
+    with caplog.at_level(logging.WARNING):
+        flag_fuel_mismatch(overrides)
+
+    # Assert
+    assert any("fuel" in r.message.lower() for r in caplog.records)
+
+
+def test_a_same_family_fuel_refinement_is_not_logged(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    # A solid-fuel room heater's natural fuel (house coal 33) is a *default* for
+    # the ambiguous solid family. A "smokeless coal" override refines it within
+    # the same family — that is expected, not a contradiction, so it must NOT log.
+    # Only a different fuel family (gas/electric on a solid heater) is flagged.
+    overrides = ResolvedPropertyOverrides(
+        rows=(
+            ResolvedPropertyOverride(
+                "main_heating_system", 0, "Solid fuel room heater, closed"
+            ),
+            ResolvedPropertyOverride("main_fuel", 0, "smokeless coal"),
+        )
+    )
+
+    # Act
+    with caplog.at_level(logging.WARNING):
+        flag_fuel_mismatch(overrides)
+
+    # Assert
+    assert caplog.records == []
diff --git a/tests/scripts/test_reclassify_heating_overrides.py b/tests/scripts/test_reclassify_heating_overrides.py
new file mode 100644
index 000000000..f3cb73382
--- /dev/null
+++ b/tests/scripts/test_reclassify_heating_overrides.py
@@ -0,0 +1,30 @@
+"""The one-time heating-override re-classification map is internally valid."""
+
+from __future__ import annotations
+
+from domain.epc.property_overlays.main_heating_system_overlay import (
+    main_heating_overlay_for,
+)
+from domain.epc.property_overrides.main_heating_system_type import (
+    MainHeatingSystemType,
+)
+from scripts.reclassify_heating_overrides import REMAP
+
+
+def test_every_remap_target_is_a_resolvable_archetype() -> None:
+    # The remap must never point a stored description at an archetype the overlay
+    # can't model — that would replace one broken value with another. Every
+    # target must decode to a real SAP heating code (ADR-0041).
+    for description, archetype in REMAP.items():
+        simulation = main_heating_overlay_for(archetype.value, 0)
+
+        assert simulation is not None, description
+        assert simulation.heating is not None, description
+        assert simulation.heating.sap_main_heating_code is not None, description
+
+
+def test_remap_targets_are_main_heating_system_members() -> None:
+    # Belt and braces: the values are enum members (a typo can't smuggle a
+    # non-archetype string into the DB).
+    for archetype in REMAP.values():
+        assert archetype in MainHeatingSystemType