diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index 0710837e..e161dbf5 100644
--- a/tests/domain/epc/test_main_heating_system_overlay.py
+++ b/tests/domain/epc/test_main_heating_system_overlay.py
@@ -8,6 +8,7 @@ from __future__ import annotations
 
 import pytest
 
+from domain.epc.main_heating_system_type import MainHeatingSystemType
 from domain.epc.property_overlays.main_fuel_overlay import fuel_overlay_for
 from domain.epc.property_overlays.main_heating_system_overlay import (
     main_heating_overlay_for,
@@ -103,3 +104,17 @@ def test_the_three_heating_overrides_compose_without_conflict() -> None:
     assert main.sap_main_heating_code == 404
     assert result.sap_heating.water_heating_code == 903
     assert result.sap_heating.water_heating_fuel == 29
+
+
+@pytest.mark.parametrize(
+    "member",
+    [m for m in MainHeatingSystemType if m is not MainHeatingSystemType.UNKNOWN],
+)
+def test_every_resolvable_main_heating_value_decodes(
+    member: MainHeatingSystemType,
+) -> None:
+    # Act
+    simulation = main_heating_overlay_for(member.value, 0)
+
+    # Assert
+    assert simulation is not None
diff --git a/tests/domain/epc/test_water_heating_overlay.py b/tests/domain/epc/test_water_heating_overlay.py
index 7dd8c2d0..6e0b1fdb 100644
--- a/tests/domain/epc/test_water_heating_overlay.py
+++ b/tests/domain/epc/test_water_heating_overlay.py
@@ -11,6 +11,7 @@ import pytest
 from domain.epc.property_overlays.water_heating_overlay import (
     water_heating_overlay_for,
 )
+from domain.epc.water_heating_type import WaterHeatingType
 from domain.modelling.scoring.overlay_applicator import apply_simulations
 from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
     build_epc,
@@ -71,3 +72,16 @@ def test_water_heating_override_remaps_the_hot_water_arrangement() -> None:
     # Assert — the calculator reads these off sap_heating.
     assert result.sap_heating.water_heating_code == 903
     assert result.sap_heating.water_heating_fuel == 29
+
+
+@pytest.mark.parametrize(
+    "member", [m for m in WaterHeatingType if m is not WaterHeatingType.UNKNOWN]
+)
+def test_every_resolvable_water_heating_value_decodes(
+    member: WaterHeatingType,
+) -> None:
+    # Act
+    simulation = water_heating_overlay_for(member.value, 0)
+
+    # Assert
+    assert simulation is not None
diff --git a/tests/repositories/property/test_override_component_consistency.py b/tests/repositories/property/test_override_component_consistency.py
new file mode 100644
index 00000000..df830cd0
--- /dev/null
+++ b/tests/repositories/property/test_override_component_consistency.py
@@ -0,0 +1,24 @@
+"""Every override component must be wired through the WHOLE chain.
+
+The finaliser reader (`_ROW_TYPES`, component -> landlord table) and the overlay
+registry (`_COMPONENT_OVERLAYS`, component -> overlay mapper) must cover exactly
+the same set of components. If a component is classified + stored but has no
+reader entry, the finaliser silently never writes its `property_overrides` rows;
+if it has no overlay entry, the row never reaches the calculator. This guard
+keeps the two registries in lock-step (it would have caught the missing
+main_fuel / glazing / construction_age_band reader entries).
+"""
+
+from __future__ import annotations
+
+from infrastructure.landlord_overrides.landlord_override_reader_postgres_repository import (  # pyright: ignore[reportPrivateUsage]
+    _ROW_TYPES,
+)
+from repositories.property.landlord_override_overlays import (  # pyright: ignore[reportPrivateUsage]
+    _COMPONENT_OVERLAYS,
+)
+
+
+def test_reader_and_overlay_registries_cover_the_same_components() -> None:
+    # Assert
+    assert set(_ROW_TYPES) == set(_COMPONENT_OVERLAYS)