diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index 5c1b680d2..45ecc9ecf 100644
--- a/tests/domain/epc/test_main_heating_system_overlay.py
+++ b/tests/domain/epc/test_main_heating_system_overlay.py
@@ -434,14 +434,27 @@ def test_storage_heaters_drag_along_conservative_manual_charge_control(
     assert simulation.heating.main_heating_category == 7
 
 
-def test_direct_acting_electric_does_not_drag_along_a_control() -> None:
-    # Charge control is a storage concept and full boiler controls are a wet-
-    # system concept; direct-acting electric panel heaters take neither, so the
-    # overlay leaves the control untouched.
-    simulation = main_heating_overlay_for("Direct-acting electric", 0)
+@pytest.mark.parametrize(
+    "main_heating_value",
+    ["Direct-acting electric", "Electric boiler", "Electric CPSU"],
+)
+def test_electric_boiler_overlays_the_boiler_category(
+    main_heating_value: str,
+) -> None:
+    # A system-replacing override must stamp the boiler heating category (SAP
+    # Table 4a Category 2 — codes 191/192 are wet electric boilers). Leaving it
+    # unset inherits the replaced system's: on portfolio 796, 30 of the first
+    # 40 live 191/192 overrides carried an inherited category — 6 (community)
+    # or 4 (heat pump) suppressed the HHRSH pathway entirely, and 7 (storage)
+    # made the Table 12a resolver bill direct-acting heat 100% at the off-peak
+    # low rate (ADR-0052, #1444).
+    # Act
+    simulation = main_heating_overlay_for(main_heating_value, 0)
+
+    # Assert — SAP Table 4a Category 2 (boiler system).
     assert simulation is not None
     assert simulation.heating is not None
-    assert simulation.heating.main_heating_control is None
+    assert simulation.heating.main_heating_category == 2
 
 
 @pytest.mark.parametrize(