diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index 40998c7d7..d9f89b4b6 100644
--- a/tests/domain/epc/test_main_heating_system_overlay.py
+++ b/tests/domain/epc/test_main_heating_system_overlay.py
@@ -233,6 +233,32 @@ def test_off_peak_underfloor_asserts_a_dual_meter(main_heating_value: str) -> No
     assert simulation.heating.meter_type == "Dual"
 
 
+@pytest.mark.parametrize(
+    "main_heating_value",
+    [
+        "Electric underfloor, in concrete slab (off-peak)",
+        "Electric underfloor, integrated storage and direct-acting",
+        "Electric underfloor, in screed above insulation",
+    ],
+)
+def test_electric_underfloor_overlays_the_underfloor_category(
+    main_heating_value: str,
+) -> None:
+    # A system-replacing override must stamp the underfloor heating category
+    # (SAP Table 4a Category 8). Leaving it unset lets the replaced system's
+    # category survive onto the effective cert — property 711795's community
+    # heating (category 6) survived an underfloor override, so the heating
+    # generator read the dwelling as a heat network and offered no heating
+    # upgrade at all, and the baseline mis-rated 51 vs 67 (ADR-0050).
+    # Act
+    simulation = main_heating_overlay_for(main_heating_value, 0)
+
+    # Assert — SAP Table 4a Category 8 (Electric underfloor heating).
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.main_heating_category == 8
+
+
 def test_screed_underfloor_defers_the_meter_to_the_cert() -> None:
     # "In screed above insulation (standard or off peak)" is tariff-ambiguous (81%
     # of the corpus lodge off-peak), so the archetype cannot know the meter — it