diff --git a/tests/domain/epc/test_main_heating_system_type.py b/tests/domain/epc/test_main_heating_system_type.py
new file mode 100644
index 000000000..b206b672b
--- /dev/null
+++ b/tests/domain/epc/test_main_heating_system_type.py
@@ -0,0 +1,33 @@
+"""Contract tests for the `MainHeatingSystemType` Landlord-Override taxonomy.
+
+The oil / solid-fuel boiler family is lock-step with the app-side
+`MainHeatingSystemValues` enum + migration 0279 (assessment-model#455, ADR-0002 /
+ADR-0067): the string values here are the shared contract and must match
+byte-for-byte. The classifier resolves a reply value to a member via
+`MainHeatingSystemType(value)`, so "is this a recognised system" is exactly that
+construction.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from domain.epc.property_overrides.main_heating_system_type import (
+    MainHeatingSystemType,
+)
+
+# The oil / solid-fuel boiler family, byte-for-byte with assessment-model#455.
+_BOILER_VALUES: list[str] = [
+    "Oil boiler, regular",
+    "Oil boiler, combi",
+    "Solid fuel boiler",
+]
+
+
+@pytest.mark.parametrize("value", _BOILER_VALUES)
+def test_oil_and_solid_fuel_boiler_string_is_a_recognised_system(value: str) -> None:
+    # Act — a missing member raises ValueError (the classifier falls to UNKNOWN).
+    member = MainHeatingSystemType(value)
+
+    # Assert — the canonical string round-trips as its own member value.
+    assert member.value == value