Slice S0380.127: resolve Elmhurst "No Access" cylinder via RdSAP 10 Table 28

Elmhurst Summary §15.1 sometimes lodges "Cylinder Size: No Access" (the
inaccessible-cylinder lodging form). Pre-slice the mapper strict-raised
`UnmappedElmhurstLabel` because `_ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10`
only carried the three lodged-size labels (Normal/Medium/Large).

Per RdSAP 10 Specification Table 28 page 55 ("Cylinder size"):

  > "Inaccessible:
  >   - if off-peak electric dual immersion: 210 litres
  >   - if from solid fuel boiler: 160 litres
  >   - otherwise: 110 litres"

And per §10.5.1 page 53:

  > "An electric immersion is assumed dual in the following cases:
  >  - cylinder is inaccessible and electricity tariff is dual"

So the 210-L "off-peak electric dual immersion" branch fires automatically
when both (a) cylinder is inaccessible AND (b) water heating is electric
AND (c) meter type is dual / off-peak (no separate dual-immersion lodging
required).

New helper `_resolve_elmhurst_inaccessible_cylinder_size` keys off
§15.0 "Water Heating Fuel Type" + §14.2 "Electricity meter type":

  - solid fuel water heating fuel (Anthracite, House coal, Wood, etc.)
    → 160 L → SAP10 cylinder_size enum 3 (Medium)
  - "Electricity" + dual/18-hour/24-hour/off-peak meter
    → 210 L → SAP10 cylinder_size enum 4 (Large)
  - otherwise → 110 L → SAP10 cylinder_size enum 2 (Normal)

`_elmhurst_cylinder_size_code` extended with optional water_heating_fuel
+ meter_type kwargs; the single call site at line 4459 threads
`survey.water_heating.water_heating_fuel_type` and
`survey.meters.electricity_meter_type`.

Property 001431 (the heating-systems corpus dwelling) lodges `pcdb 1`
with §14.0 Potterton oil boiler (PCDF 716) + §15.0 "Water Heating Fuel
Type: Heating oil" + §14.2 "Electricity meter type: 18 Hour" — water
fuel is oil (not electric, not solid fuel) → "otherwise" branch → 110 L
→ enum 2 (Normal). `pcdb 1` now cascade-executes (corpus tally 34 → 35
OK / 41 populated).

Extended handover suite at HEAD post-slice: **831 pass, 0 fail**
(was 830 + 1 new AAA test).

Pyright net-zero on touched files (45 → 45 — pre-existing errors
unrelated).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -236,6 +236,39 @@ def test_summary_001479_mapper_extensions_count_matches_extension_bps() -> None:
     assert len(epc.sap_building_parts) == 3
 
 
+def test_summary_001431_pcdb_1_inaccessible_cylinder_resolves_to_normal_per_rdsap_10_table_28() -> None:
+    # Arrange — Heating-systems corpus fixture 001431 / "pcdb 1" lodges
+    # §15.1 "Cylinder Size: No Access" (the Elmhurst inaccessible-cylinder
+    # lodging form). Per RdSAP 10 Specification Table 28 page 55:
+    #
+    #   "Inaccessible:
+    #     - if off-peak electric dual immersion: 210 litres
+    #     - if from solid fuel boiler: 160 litres
+    #     - otherwise: 110 litres"
+    #
+    # pcdb 1 lodges §14.0 Main Heating as a Potterton oil boiler (PCDF
+    # 716) + §15.0 Water Heating Fuel Type "Heating oil" → not an
+    # electric dual immersion, not a solid fuel boiler → the spec's
+    # "otherwise" branch → **110 litres** = SAP10 cylinder_size enum 2
+    # (Normal per `_ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10`).
+    #
+    # Pre-slice the mapper strict-raised `UnmappedElmhurstLabel` on the
+    # "No Access" string because `_elmhurst_cylinder_size_code` only
+    # carried the three lodged-size dict entries (Normal/Medium/Large).
+    summary_pdf = (
+        Path(__file__).parents[3]
+        / "sap worksheets/heating systems examples/pcdb 1/Summary_001431.pdf"
+    )
+    pages = _summary_pdf_to_textract_style_pages(summary_pdf)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert
+    assert epc.sap_heating.cylinder_size == 2
+
+
 def test_summary_001431_electric_1_underfloor_heating_resolves_to_in_screed_per_rdsap_10_section_10_11() -> None:
     # Arrange — Heating-systems corpus fixture 001431 / "electric 1" lodges
     # §14.0 "Heat Emitter: Underfloor Heating" (bare form, no subtype

datatypes/epc/domain/mapper.py

@@ -4127,8 +4127,73 @@ _ELMHURST_CYLINDER_INSULATION_LABEL_TO_SAP10: Dict[str, int] = {
 }
 
 
+# Elmhurst §15.0 "Water Heating Fuel Type" labels that route to solid-
+# fuel Table 32 codes (Anthracite, House coal, Wood logs/pellets, etc.).
+# Used by `_resolve_elmhurst_inaccessible_cylinder_size` to detect the
+# "from solid fuel boiler" branch of RdSAP 10 Table 28 page 55.
+_ELMHURST_SOLID_FUEL_WATER_HEATING_LABELS: frozenset[str] = frozenset({
+    "Anthracite",
+    "House coal",
+    "Manufactured smokeless fuel",
+    "Wood logs",
+    "Wood pellets",
+    "Wood chips",
+    "Dual fuel (mineral and wood)",
+    "Coal",
+})
+
+# Elmhurst §14.2 "Electricity meter type" labels that signify off-peak
+# / dual metering (where an inaccessible electric immersion is assumed
+# dual per RdSAP 10 §10.5.1 → Table 28 "off-peak electric dual
+# immersion" 210 L branch).
+_ELMHURST_DUAL_OFF_PEAK_METER_LABELS: frozenset[str] = frozenset({
+    "Dual",
+    "Dual (24 hour)",
+    "18 Hour",
+    "Off-peak 18 hour",
+    "10 Hour",
+})
+
+
+def _resolve_elmhurst_inaccessible_cylinder_size(
+    water_heating_fuel_label: str,
+    meter_type_label: str,
+) -> int:
+    """RdSAP 10 Specification Table 28 page 55 — derive cylinder size
+    when §15.1 lodges "No Access" / Inaccessible.
+
+    Spec rule verbatim:
+
+      "Inaccessible:
+        - if off-peak electric dual immersion: 210 litres
+        - if from solid fuel boiler: 160 litres
+        - otherwise: 110 litres"
+
+    Returns SAP10 cylinder_size enum (per
+    `_ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10`):
+      2 (Normal)  → 110 L — modal "otherwise" branch
+      3 (Medium)  → 160 L — solid fuel boiler
+      4 (Large)   → 210 L — off-peak electric dual immersion
+
+    Per RdSAP 10 §10.5.1: "An electric immersion is assumed dual in the
+    following cases: cylinder is inaccessible and electricity tariff
+    is dual" — so the 210-L branch fires automatically when both
+    conditions hold (no separate "is_dual_immersion" lodging needed).
+    """
+    if water_heating_fuel_label in _ELMHURST_SOLID_FUEL_WATER_HEATING_LABELS:
+        return 3  # Medium / 160 L
+    is_electric = water_heating_fuel_label.startswith("Electricity")
+    is_off_peak = meter_type_label in _ELMHURST_DUAL_OFF_PEAK_METER_LABELS
+    if is_electric and is_off_peak:
+        return 4  # Large / 210 L
+    return 2  # Normal / 110 L
+
+
 def _elmhurst_cylinder_size_code(
-    cylinder_size_label: Optional[str], cylinder_present: bool,
+    cylinder_size_label: Optional[str],
+    cylinder_present: bool,
+    water_heating_fuel_label: Optional[str] = None,
+    meter_type_label: Optional[str] = None,
 ) -> Optional[int]:
     """Map an Elmhurst §15.1 "Cylinder Size" label to the SAP10
     cascade enum. Returns None when no cylinder is present or the
@@ -4136,9 +4201,25 @@ def _elmhurst_cylinder_size_code(
     `UnmappedElmhurstLabel` when the label IS lodged but isn't in
     `_ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10` — that's a mapper-coverage
     gap that should be made explicit so the next fixture forces a dict
-    entry, not silently routed off the HW-with-cylinder cascade path."""
+    entry, not silently routed off the HW-with-cylinder cascade path.
+
+    The bare lodging "No Access" (Inaccessible) routes through
+    `_resolve_elmhurst_inaccessible_cylinder_size` per RdSAP 10
+    Table 28 page 55."""
     if not cylinder_present or cylinder_size_label is None:
         return None
+    if cylinder_size_label == "No Access":
+        if water_heating_fuel_label is None or meter_type_label is None:
+            raise UnmappedElmhurstLabel(
+                "cylinder_size",
+                (
+                    "lodged 'No Access' requires water_heating fuel + "
+                    "meter context to apply RdSAP 10 Table 28 (p.55)"
+                ),
+            )
+        return _resolve_elmhurst_inaccessible_cylinder_size(
+            water_heating_fuel_label, meter_type_label,
+        )
     code = _ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10.get(cylinder_size_label)
     if code is None:
         raise UnmappedElmhurstLabel("cylinder_size", cylinder_size_label)
@@ -4459,6 +4540,8 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
         cylinder_size=_elmhurst_cylinder_size_code(
             survey.water_heating.cylinder_size_label,
             survey.water_heating.hot_water_cylinder_present,
+            water_heating_fuel_label=survey.water_heating.water_heating_fuel_type,
+            meter_type_label=survey.meters.electricity_meter_type,
         ),
         cylinder_insulation_type=_elmhurst_cylinder_insulation_code(
             survey.water_heating.cylinder_insulation_label,