diff --git a/domain/epc/property_overlays/main_heating_system_overlay.py b/domain/epc/property_overlays/main_heating_system_overlay.py
index 14ca6b6bf..a2d9bc634 100644
--- a/domain/epc/property_overlays/main_heating_system_overlay.py
+++ b/domain/epc/property_overlays/main_heating_system_overlay.py
@@ -68,6 +68,17 @@ _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))
+
 # 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
@@ -130,6 +141,17 @@ def _control_for(code: int) -> Optional[int]:
         return _MANUAL_CHARGE_CONTROL
     if code in _GAS_BOILER_CODES:
         return _FULL_BOILER_CONTROL
+    if code in _SOLID_FUEL_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 _SOLID_FUEL_ROOM_HEATER_CODES:
+        return _ROOM_HEATER_CATEGORY
     return None
 
 
@@ -163,6 +185,7 @@ def main_heating_overlay_for(
     return EpcSimulation(
         heating=HeatingOverlay(
             sap_main_heating_code=code,
+            main_heating_category=_category_for(code),
             meter_type=_meter_for(code),
             main_heating_control=_control_for(code),
             # A landlord override describes the existing dwelling, so its assumed