diff --git a/datatypes/epc/domain/tests/test_from_sap_schema.py b/datatypes/epc/domain/tests/test_from_sap_schema.py
index 0e9c5bc92..1f6afae21 100644
--- a/datatypes/epc/domain/tests/test_from_sap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_sap_schema.py
@@ -116,6 +116,17 @@ class TestFromSapSchema17_1RebaselineFields:
 
         assert result.built_form == "1"
 
+    def test_maps_secondary_heating_element(self) -> None:
+        # secondary_heating is read by the calculator (cert_to_inputs) — dropping
+        # it under-counts a real secondary heater. The fixture lodges "None" (no
+        # secondary); assert it's carried through rather than silently dropped.
+        schema = from_dict(SapSchema17_1, load("sap_17_1.json"))
+
+        result = EpcPropertyDataMapper.from_sap_schema_17_1(schema)
+
+        assert result.secondary_heating is not None
+        assert result.secondary_heating.description == "None"
+
 
 class TestFullSapHasHotWaterCylinderFallback:
     """Some full-SAP certs (e.g. SAP-Schema-17.0 cert 8265-7433-3220-9736-7902)