Map PasHub secondary-heating fuel to a SAP10 fuel code

secondary_fuel_type was hardcoded None in the from_site_notes mapper,
dropping the fuel for the ~67 Guinness GMCA 205 properties that lodge a
"Panel, convector or radiant heaters" secondary heater. Adds
_pashub_secondary_fuel_code (ADR-0015 pattern, mirrors
_pashub_main_fuel_code) mapping "Electricity" -> SAP10 code 30, with
"No Secondary Heating"/blank -> None and unknown labels strict-raising
UnmappedPasHubLabel.

Fixes #1564

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

datatypes/epc/domain/mapper.py

@@ -6042,12 +6042,7 @@ def _map_sap_heating(
     main = heating.main_heating
     secondary = heating.secondary_heating
 
-    # secondary_fuel_type is an int code in the domain model; we can't map a
-    # site-notes string directly, so leave it None unless there is secondary heating.
-    # The string fuel type is preserved via sap_heating when needed.
-    secondary_fuel_type = (
-        None if secondary.secondary_fuel == "No Secondary Heating" else None
-    )
+    secondary_fuel_type = _pashub_secondary_fuel_code(secondary.secondary_fuel)
 
     shower_outlets = (
         ShowerOutlets(
@@ -7115,6 +7110,28 @@ _PASHUB_MAIN_FUEL_TO_SAP10: Dict[str, int] = {
     "Electricity": 30,  # the standard-electricity fuel code
 }
 
+# PasHub surveyed secondary-heating `secondary_fuel` label → SAP 10.2 Table 32
+# fuel code that `secondary_fuel_type` (an int in the domain model) consumes.
+# "No Secondary Heating" is the no-secondary-heater shape and maps to None,
+# not a fuel code.
+_PASHUB_SECONDARY_FUEL_TO_SAP10: Dict[str, int] = {
+    "Electricity": 30,  # standard electricity, Table 32 code 30
+}
+
+
+def _pashub_secondary_fuel_code(fuel_label: str) -> Optional[int]:
+    """Resolve a PasHub surveyed secondary-heating Fuel label to a SAP10
+    Table 32 fuel code at the mapper boundary (ADR-0015). "No Secondary
+    Heating" is the no-secondary-heater shape and maps to None; a non-empty
+    label the lookup does not cover strict-raises `UnmappedPasHubLabel` so
+    the gap is fixed here, never silently mis-billed downstream."""
+    if not fuel_label or fuel_label == "No Secondary Heating":
+        return None
+    code = _PASHUB_SECONDARY_FUEL_TO_SAP10.get(fuel_label)
+    if code is None:
+        raise UnmappedPasHubLabel("secondary fuel", fuel_label)
+    return code
+
 
 def _pashub_main_fuel_code(fuel_label: str) -> Union[int, str]:
     """Resolve a PasHub surveyed main-heating Fuel label to a SAP10 fuel code

datatypes/epc/domain/tests/test_from_site_notes.py

@@ -113,6 +113,41 @@ class TestWallConstructionCoding:
             EpcPropertyDataMapper.from_site_notes(survey)
 
 
+class TestSecondaryFuelTypeCoding:
+    """`from_site_notes` must int-code the PAS Hub secondary-heating
+    `secondary_fuel` label to the SAP 10.2 Table 32 `secondary_fuel_type`
+    code, not leave it hardcoded `None`. ~67/205 Guinness cohort properties
+    lodge a "Panel, convector or radiant heaters" secondary heater whose
+    fuel was silently dropped (issue #1564).
+    """
+
+    @pytest.mark.parametrize(
+        "label, expected_code",
+        [
+            ("Electricity", 30),  # standard electricity, Table 32 code 30
+            ("No Secondary Heating", None),  # no secondary heater lodged
+            ("", None),  # no lodging
+        ],
+    )
+    def test_label_maps_to_sap_code(
+        self, label: str, expected_code: Optional[int]
+    ) -> None:
+        data = load("pashub_rdsap_site_notes_example1.json")
+        data["heating_and_hot_water"]["secondary_heating"]["secondary_fuel"] = label
+        survey = from_dict(PasHubRdSapSiteNotes, data)
+        result = EpcPropertyDataMapper.from_site_notes(survey)
+        assert result.sap_heating.secondary_fuel_type == expected_code
+
+    def test_unknown_label_strict_raises(self) -> None:
+        data = load("pashub_rdsap_site_notes_example1.json")
+        data["heating_and_hot_water"]["secondary_heating"][
+            "secondary_fuel"
+        ] = "Bulk LPG"
+        survey = from_dict(PasHubRdSapSiteNotes, data)
+        with pytest.raises(UnmappedPasHubLabel):
+            EpcPropertyDataMapper.from_site_notes(survey)
+
+
 class TestWallInsulationTypeCoding:
     """`from_site_notes` must int-code the PAS Hub `walls_insulation_type` label
     to the SAP10 wall-insulation code `u_wall` consumes (matching the Elmhurst