diff --git a/domain/epc/property_overrides/main_heating_guard.py b/domain/epc/property_overrides/main_heating_guard.py
index 9eb50548b..8347651bf 100644
--- a/domain/epc/property_overrides/main_heating_guard.py
+++ b/domain/epc/property_overrides/main_heating_guard.py
@@ -8,17 +8,34 @@ from domain.epc.property_overrides.main_heating_system_type import (
 
 
 def main_heating_guard(description: str) -> Optional[MainHeatingSystemType]:
-    """Deterministically resolve a High Heat Retention Storage Heater (HHRSH)
-    description, which the LLM funnelled into ``"Electric storage heaters, old"``
-    (SAP 401) for want of an HHRSH archetype (#1376 / ADR-0044).
+    """Deterministically resolve the structured main-heating descriptions the LLM
+    funnelled into a garbage-drawer archetype for want of a correct target (#1376).
 
-    HHRSH is a distinct RdSAP system (SAP Table 4a 409) with its own intrinsic
-    charge control (2404) — the *best* modern storage, not the *worst* old large-
-    volume type. This guard claims only the structured HHRSH phrasing and returns
-    ``None`` for every other description (the remaining storage subtypes the LLM
-    already classifies correctly, and varied phrasings), so they still reach the
-    LLM classifier via ``GuardedColumnClassifier``.
+    Two dumping grounds are rescued:
+
+    - **HHRSH** (ADR-0044): ``"…High heat retention storage heaters"`` went to
+      ``"Electric storage heaters, old"`` (SAP 401) — the *worst* old type. HHRSH is
+      SAP Table 4a 409 with its own intrinsic charge control (2404).
+    - **Gas CPSU** (ADR-0045): the mains-gas CPSU garbage drawer also held
+      solid-fuel room heaters (open fire 631 / + back boiler 632 / closed + boiler
+      634) and electric ``"NA"``-type boilers (SAP 191). "NA" is the boiler-type
+      value meaning "not a gas combi/regular/CPSU", i.e. an electric boiler.
+
+    Returns ``None`` for descriptions the LLM already classifies correctly (genuine
+    gas boilers, other storage subtypes, a plain closed room heater) and for varied
+    phrasings, so they still reach the LLM via ``GuardedColumnClassifier``. Order
+    matters: the back-boiler open fire is tested before the bare open fire it
+    contains.
     """
-    if "high heat retention" in description.lower():
+    text = description.lower()
+    if "high heat retention" in text:
         return MainHeatingSystemType.ELECTRIC_STORAGE_HIGH_HEAT_RETENTION
+    if "rated na" in text:
+        return MainHeatingSystemType.ELECTRIC_BOILER
+    if "open fire" in text and "back boiler" in text:
+        return MainHeatingSystemType.SOLID_FUEL_ROOM_HEATER_OPEN_FIRE_BACK_BOILER
+    if "open fire" in text:
+        return MainHeatingSystemType.SOLID_FUEL_ROOM_HEATER_OPEN_FIRE
+    if "closed room heater" in text and "with boiler" in text:
+        return MainHeatingSystemType.SOLID_FUEL_ROOM_HEATER_CLOSED_WITH_BOILER
     return None