diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index f33efe3c6..b100f75a6 100644
--- a/tests/domain/epc/test_main_heating_system_overlay.py
+++ b/tests/domain/epc/test_main_heating_system_overlay.py
@@ -111,6 +111,22 @@ def test_high_heat_retention_storage_decodes_to_its_own_code_not_old_storage() -
     assert simulation.heating.sap_main_heating_code == 409
 
 
+def test_high_heat_retention_storage_drags_its_intrinsic_companions() -> None:
+    # HHRSH has a single intrinsic charge control (Table 4e 2404, 0 C adjustment),
+    # so — unlike a generic storage heater whose control is unobserved — it must
+    # NOT drag the conservative manual default (2401, +0.7 C penalty), which would
+    # under-credit it. It is electric, on an off-peak (Dual) meter (ADR-0044).
+    simulation = main_heating_overlay_for(
+        "Electric storage heaters, high heat retention", 0
+    )
+
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.main_heating_control == 2404
+    assert simulation.heating.main_fuel_type == 29
+    assert simulation.heating.meter_type == "Dual"
+
+
 @pytest.mark.parametrize(
     "main_heating_value",
     [