diff --git a/backend/documents_parser/elmhurst_extractor.py b/backend/documents_parser/elmhurst_extractor.py
index 1bb3b3c2..061d972f 100644
--- a/backend/documents_parser/elmhurst_extractor.py
+++ b/backend/documents_parser/elmhurst_extractor.py
@@ -1044,6 +1044,19 @@ class ElmhurstSiteNotesExtractor:
         lines = self._section_lines("14.0 Main Heating1", "14.1 Main Heating2")
         pct_raw = self._local_val(lines, "Percentage of Heat")
         pct = int(pct_raw.split()[0]) if pct_raw else 0
+        # §14.0 "Main Heating SAP Code" identifies Main 1 by SAP 10.2
+        # Table 4a code (e.g. 224 = "Air source heat pump, 2013 or
+        # later"). PCDB-boiler certs leave this empty / lodge "0" — the
+        # PCDB index in `PCDF boiler Reference` is the identifier in
+        # that case. Treat 0 (or absent) as None so the mapper can
+        # distinguish "no SAP code lodged" from a real Table 4a code.
+        sap_code_raw = self._local_val(lines, "Main Heating SAP Code")
+        main_heating_sap_code: Optional[int] = None
+        if sap_code_raw is not None:
+            head = sap_code_raw.split()[0] if sap_code_raw.split() else ""
+            if head.isdigit():
+                v = int(head)
+                main_heating_sap_code = v if v > 0 else None
         # The "Secondary Heating SapCode" key is lodged inside §14.1 Main
         # Heating2 — Elmhurst uses the Main-2 block to also carry the
         # cert's secondary heating system (when one exists). Look for it
@@ -1069,6 +1082,7 @@ class ElmhurstSiteNotesExtractor:
             percentage_of_heat=pct,
             pcdf_boiler_reference=self._local_val(lines, "PCDF boiler Reference"),
             heat_pump_age=self._local_val(lines, "Heat pump age"),
+            main_heating_sap_code=main_heating_sap_code,
             secondary_heating_sap_code=secondary_code,
         )
 
diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 1e5cec98..963f5abc 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -3826,6 +3826,24 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
     heat_emitter_int = _elmhurst_heat_emitter_int(mh.heat_emitter)
     sap_control_int = _elmhurst_sap_control_code(sap_control)
     main_heating_category = _elmhurst_main_heating_category(mh, pcdb_index)
+    # Strict-raise mirror of [[unmapped-api-code]] — when Main 1 has
+    # neither a PCDB boiler reference nor a lodged Table 4a SAP code,
+    # the mapper has no identifier for the heat source and the cascade
+    # would silently fall back to the 0.80 gas-boiler default. First
+    # surfaced on cert 000565 where Main 1 is a heat pump lodging
+    # `PCDF boiler Reference = 0` + `Main Heating SAP Code = 224`; if
+    # the extractor (or a future variant cert) drops both, raise so the
+    # gap surfaces here instead of as a SAP-delta residual downstream.
+    if mh.main_heating_sap_code is None and pcdb_index is None:
+        raise UnmappedElmhurstLabel(
+            "main_heating",
+            (
+                f"§14.0 Main Heating1 has neither PCDF boiler reference "
+                f"({mh.pcdf_boiler_reference!r}) nor SAP code "
+                f"({mh.main_heating_sap_code!r}); cannot identify the "
+                f"heat source"
+            ),
+        )
     # Shower-outlet classification: SAP10.2 Appendix J routes electric
     # showers via §J line 64a (their own kWh stream) and treats mixer
     # showers as drawing from the HW system. The Summary PDF lodges
@@ -3874,6 +3892,12 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
                 # number drives PCDB lookup in the cascade.
                 main_heating_index_number=pcdb_index,
                 main_heating_data_source=1 if pcdb_index is not None else None,
+                # §14.0 "Main Heating SAP Code" — Table 4a integer
+                # identifying Main 1 when no PCDB boiler reference is
+                # lodged (e.g. heat pump SAP code 224 on cert 000565).
+                # The cascade's `seasonal_efficiency` reads this when
+                # there is no PCDB Table 105/362 record to override.
+                sap_main_heating_code=mh.main_heating_sap_code,
             )
         ],
         has_fixed_air_conditioning=survey.ventilation.fixed_space_cooling,
diff --git a/datatypes/epc/surveys/elmhurst_site_notes.py b/datatypes/epc/surveys/elmhurst_site_notes.py
index fa87f167..7c5396a0 100644
--- a/datatypes/epc/surveys/elmhurst_site_notes.py
+++ b/datatypes/epc/surveys/elmhurst_site_notes.py
@@ -204,6 +204,14 @@ class MainHeating:
         None  # e.g. "17742 Potterton, Promax 33 Combi ErP, 88.30%"
     )
     heat_pump_age: Optional[str] = None
+    # Section 14.0 "Main Heating SAP Code" — the SAP 10.2 Table 4a code
+    # identifying Main 1 when no PCDB boiler reference is lodged (e.g.
+    # heat pump certs lodge `PCDF boiler Reference = 0` + SAP code = 224
+    # for "Air source heat pump, 2013 or later"). None when the line is
+    # absent or lodged as 0 (= "no code lodged"; PCDB-listed boilers
+    # leave §14.0 SAP code empty and identify themselves via the PCDB
+    # index instead).
+    main_heating_sap_code: Optional[int] = None
     # Section 14.0 also lodges a secondary heating system (when one is
     # installed). The SAP code is the integer the cascade reads via
     # `SapHeating.secondary_heating_type` to apply the Table 11