diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index a9f9e5cae..b3bfdb370 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -7070,10 +7070,15 @@ _PASHUB_MAIN_FUEL_TO_SAP10: Dict[str, int] = {
 def _pashub_main_fuel_code(fuel_label: str) -> Union[int, str]:
     """Resolve a PasHub surveyed main-heating Fuel label to a SAP10 fuel code
     at the mapper boundary (ADR-0015). A genuinely blank label is the "no main
-    heating" shape and passes through unchanged."""
+    heating" shape and passes through unchanged; 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:
         return fuel_label
-    return _PASHUB_MAIN_FUEL_TO_SAP10.get(fuel_label, fuel_label)
+    code = _PASHUB_MAIN_FUEL_TO_SAP10.get(fuel_label)
+    if code is None:
+        raise UnmappedPasHubLabel("main fuel", fuel_label)
+    return code
 
 
 def _resolve_elmhurst_underfloor_subtype(