A community override keeps an assessor-observed Group 3 control 🟩

The heat-network mirror of keep_existing_off_peak_meter: the override's
2313 default applies only when the replaced system's control is
cross-family (stale); an observed community control survives.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

domain/epc/property_overlays/main_heating_system_overlay.py

@@ -445,5 +445,10 @@ def main_heating_overlay_for(
             # (e.g. a 24-hour all-low tariff). Measures, which re-meter for real,
             # build their HeatingOverlay directly and leave this False.
             keep_existing_off_peak_meter=True,
+            # Likewise a heat-network override's control default (2313) must
+            # not overwrite an assessor-OBSERVED Group 3 control on a community
+            # cert being confirmed — only a stale cross-family control is
+            # replaced (ADR-0053).
+            keep_existing_heat_network_control=code in _HEAT_NETWORK_CODES,
         )
     )

domain/modelling/scoring/overlay_applicator.py

@@ -152,6 +152,13 @@ _SAP_HEATING_FIELDS: tuple[str, ...] = (
 _ENERGY_SOURCE_FIELDS: tuple[str, ...] = ("meter_type", "gas_connection_available")
 
 
+def _is_heat_network_control(control: object) -> bool:
+    """True iff the lodged control is a SAP Table 4e Group 3 (heat network)
+    code — 2301-2314 — i.e. an assessor-observed community control a
+    heat-network override's default must not overwrite (ADR-0053)."""
+    return isinstance(control, int) and 2301 <= control <= 2314
+
+
 def _is_off_peak_meter(meter_type: object) -> bool:
     """True iff the meter resolves to an off-peak Table 12a tariff (not the
     STANDARD single-rate column). Unparseable / absent meters count as not
@@ -177,8 +184,21 @@ def _fold_heating(epc: EpcPropertyData, overlay: HeatingOverlay) -> None:
     main = epc.sap_heating.main_heating_details[0]
     for field_name in _MAIN_HEATING_FIELDS:
         value = getattr(overlay, field_name)
-        if value is not None:
-            setattr(main, field_name, value)
+        if value is None:
+            continue
+        # A community override's control is a coherent default, not an observed
+        # one: when it opts in (`keep_existing_heat_network_control`) and the
+        # cert already lodges a Table 4e GROUP 3 control (assessor-observed on
+        # a community cert being confirmed), keep the cert's. A cross-family
+        # control (boiler 2110, storage 2401) is stale and is still replaced
+        # (ADR-0053).
+        if (
+            field_name == "main_heating_control"
+            and overlay.keep_existing_heat_network_control
+            and _is_heat_network_control(main.main_heating_control)
+        ):
+            continue
+        setattr(main, field_name, value)
     # `main_heating_index_number` (PCDB-resolved, e.g. a heat pump) and
     # `sap_main_heating_code` (Table 4a-resolved, e.g. storage heaters) are
     # mutually-exclusive efficiency anchors: a whole-system replacement to one

domain/modelling/simulation.py

@@ -200,6 +200,15 @@ class HeatingOverlay:
     # MEASURE re-meters for real (Elmhurst re-lodges 18-hour → Dual on a storage
     # install), so it leaves this False. `_fold_heating` reads it.
     keep_existing_off_peak_meter: bool = False
+    # The community-heating mirror of the flag above (ADR-0053): a heat-network
+    # override's `main_heating_control` is a coherent DEFAULT, not an observed
+    # control — when the cert already lodges a Table 4e Group 3 control the
+    # assessor observed it (a community cert being confirmed, not replaced), so
+    # the default must not overwrite it (e.g. a usage-linked 2306 downgraded to
+    # flat-rate 2313 destroys ~1-2 real SAP). A cross-family control (a boiler
+    # 2110, storage 2401) is stale by definition and is still replaced.
+    # `_fold_heating` reads it.
+    keep_existing_heat_network_control: bool = False
 
 
 @dataclass(frozen=True)