BoilerFaultCodesECA 121 Fault Code
The ECA 121 fault code means: your boiler is struggling to get the water in your radiators up to the required temperature, meaning your heating may feel lukewarm or fail to warm up properly.. It appears on 1 ECA model in our database.
Technical description: Heating circuit 1 flow water temperature not reached
DIY fix possible
Check that all radiator valves are fully openEnsure the system pressure is between 1.0 and 1.5 bar on the pressure gaugeBleed all radiators to remove trapped air pockets
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ECA models that show the 121 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
ECA 121 fault code information on this page is sourced and cross-checked against the official ECA service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026