diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index c44ffb4c..7f69e058 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -1561,4 +1561,5 @@ def _map_sap_heating(
         has_fixed_air_conditioning=ventilation.has_fixed_air_conditioning,
         secondary_fuel_type=secondary_fuel_type,
         shower_outlets=shower_outlets,
+        cylinder_insulation_thickness=heating.water_heating.insulation_thickness_mm,
     )