diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 16b52686b..244ac76ae 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -6695,6 +6695,11 @@ _PASHUB_SECONDARY_HEATING_TYPE_TO_SAP10: Dict[str, int] = {
     # (no qualifier in the label) — PCDB 601, eff 50%. 602 (601 + back boiler)
     # rejected: no back-boiler qualifier surveyed.
     "Pre 1980 - Open front fire with open flue": 601,
+    # Balanced-flue (room-sealed) gas fire/wall heater — PCDB 609 ("Gas fire
+    # or wall heater, balanced flue", flue RS, eff 58%), the only
+    # balanced-flue code in the 601-613 gas block; distinct from the
+    # open-flue codes above.
+    "Fire or wall heater with balanced flue": 609,
     # Solid fuel (eff 0.32 column B).
     "Open fire in grate": 631,
 }