diff --git a/domain/epc/property_overrides/main_heating_guard.py b/domain/epc/property_overrides/main_heating_guard.py
index 8347651bf..bf69d42c0 100644
--- a/domain/epc/property_overrides/main_heating_guard.py
+++ b/domain/epc/property_overrides/main_heating_guard.py
@@ -20,6 +20,10 @@ def main_heating_guard(description: str) -> Optional[MainHeatingSystemType]:
       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.
+    - **Electric underfloor** (ADR-0046): dumped into Direct-acting (191) / old
+      storage (401) for want of the dedicated SAP underfloor codes — in concrete
+      slab (421, off-peak), integrated storage+direct-acting (422), in screed (424,
+      meter deferred to the cert).
 
     Returns ``None`` for descriptions the LLM already classifies correctly (genuine
     gas boilers, other storage subtypes, a plain closed room heater) and for varied
@@ -30,6 +34,14 @@ def main_heating_guard(description: str) -> Optional[MainHeatingSystemType]:
     text = description.lower()
     if "high heat retention" in text:
         return MainHeatingSystemType.ELECTRIC_STORAGE_HIGH_HEAT_RETENTION
+    if "underfloor" in text:
+        if "concrete slab" in text:
+            return MainHeatingSystemType.ELECTRIC_UNDERFLOOR_SLAB_OFF_PEAK
+        if "integrated" in text:
+            return MainHeatingSystemType.ELECTRIC_UNDERFLOOR_INTEGRATED
+        if "screed" in text:
+            return MainHeatingSystemType.ELECTRIC_UNDERFLOOR_SCREED
+        return None
     if "rated na" in text:
         return MainHeatingSystemType.ELECTRIC_BOILER
     if "open fire" in text and "back boiler" in text: