diff --git a/domain/epc/property_overlays/main_heating_system_overlay.py b/domain/epc/property_overlays/main_heating_system_overlay.py
index 636fa6191..f02839105 100644
--- a/domain/epc/property_overlays/main_heating_system_overlay.py
+++ b/domain/epc/property_overlays/main_heating_system_overlay.py
@@ -134,6 +134,10 @@ _MAIN_HEATING_CODES: dict[str, int] = {
     "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,
 }
 
 
diff --git a/domain/epc/property_overrides/main_heating_system_type.py b/domain/epc/property_overrides/main_heating_system_type.py
index 2ea81c924..91e3b6f24 100644
--- a/domain/epc/property_overrides/main_heating_system_type.py
+++ b/domain/epc/property_overrides/main_heating_system_type.py
@@ -26,4 +26,5 @@ class MainHeatingSystemType(Enum):
     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"
     UNKNOWN = "Unknown"
diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index 41cc484a1..4726d6866 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)