diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 482ce2723..5c785343f 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -6032,7 +6032,7 @@ def _map_sap_heating(
             MainHeatingDetail(
                 has_fghrs=main.flue_gas_heat_recovery_system,
                 main_fuel_type=_pashub_main_fuel_code(fuel_type),
-                heat_emitter_type=main.emitter,
+                heat_emitter_type=_pashub_heat_emitter_code(main.emitter),
                 emitter_temperature=main.emitter_temperature,
                 fan_flue_present=main.fan_assist,
                 main_heating_control=main.controls,
@@ -7085,6 +7085,18 @@ def _pashub_main_fuel_code(fuel_label: str) -> Union[int, str]:
     return code
 
 
+def _pashub_heat_emitter_code(emitter_label: str) -> Union[int, str]:
+    """Resolve a PasHub surveyed main-heating emitter label to its SAP10 emitter
+    code at the mapper boundary (ADR-0015), reusing the Elmhurst emitter map
+    (`Radiators -> 1`). A blank label passes through unchanged; a non-empty label
+    the map does not cover strict-raises `UnmappedPasHubLabel` here rather than
+    resurfacing downstream as the calculator's `UnmappedSapCode: heat_emitter_type`."""
+    if not emitter_label:
+        return emitter_label
+    code = _ELMHURST_HEAT_EMITTER_TO_SAP10.get(emitter_label)
+    if code is None:
+        raise UnmappedPasHubLabel("heat emitter", emitter_label)
+    return code
 # PasHub surveyed `party_wall_construction_type` label → SAP10 party-wall code
 # (RdSAP 10 §5.10 Table 15) that `u_party_wall` consumes. Same target codes as
 # the GOV.UK-API (`_API_PARTY_WALL_CONSTRUCTION_TO_SAP10`) and Elmhurst
diff --git a/datatypes/epc/domain/tests/test_from_site_notes.py b/datatypes/epc/domain/tests/test_from_site_notes.py
index 99dba4cff..843c2a96f 100644
--- a/datatypes/epc/domain/tests/test_from_site_notes.py
+++ b/datatypes/epc/domain/tests/test_from_site_notes.py
@@ -205,10 +205,9 @@ class TestFromSiteNotesExample1:
         assert result.sap_heating.main_heating_details[0].main_fuel_type == 26
 
     def test_main_heating_emitter(self, result: EpcPropertyData) -> None:
-        # heating_and_hot_water.main_heating.emitter: "Radiators"
-        assert (
-            result.sap_heating.main_heating_details[0].heat_emitter_type == "Radiators"
-        )
+        # heating_and_hot_water.main_heating.emitter: "Radiators" is normalized
+        # at the mapper boundary to SAP10 emitter code 1 (matching Elmhurst).
+        assert result.sap_heating.main_heating_details[0].heat_emitter_type == 1
 
     def test_main_heating_no_fghrs(self, result: EpcPropertyData) -> None:
         # heating_and_hot_water.main_heating.flue_gas_heat_recovery_system: false
@@ -420,7 +419,7 @@ class TestFromSiteNotesExample1:
                     MainHeatingDetail(
                         has_fghrs=False,
                         main_fuel_type=26,
-                        heat_emitter_type="Radiators",
+                        heat_emitter_type=1,
                         emitter_temperature="Unknown",
                         fan_flue_present=True,
                         main_heating_control="Programmer, room thermostat and TRVs",
@@ -899,3 +898,25 @@ class TestPasHubUnmappedMainFuel:
 
         # Assert
         assert result.sap_heating.main_heating_details[0].main_fuel_type == 30
+
+
+class TestPasHubUnmappedHeatEmitter:
+    """A PasHub survey whose surveyed main-heating emitter label the mapper does
+    not yet cover must strict-raise `UnmappedPasHubLabel` at the boundary,
+    naming the label — so a coverage gap is fixed here (a one-line lookup
+    addition) rather than passed downstream as a raw string to resurface as the
+    calculator's `UnmappedSapCode: heat_emitter_type`.
+    """
+
+    def test_unrecognised_emitter_label_raises_naming_the_label(self) -> None:
+        # Arrange — an example fixture whose emitter cell carries a label the
+        # Elmhurst emitter map does not cover.
+        from datatypes.epc.domain.mapper import UnmappedPasHubLabel
+
+        raw = load("pashub_rdsap_site_notes_example1.json")
+        raw["heating_and_hot_water"]["main_heating"]["emitter"] = "Skirting heaters"
+        survey = from_dict(PasHubRdSapSiteNotes, raw)
+
+        # Act / Assert
+        with pytest.raises(UnmappedPasHubLabel, match="Skirting heaters"):
+            EpcPropertyDataMapper.from_site_notes(survey)