Boiler Fault Code 52:1

Also written as 521 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 52:1 appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is struggling to accurately measure the water temperature in a specific part of your heating system, which may cause your heating to run inefficiently or not at all. (As reported on Viessmann Vitodens 200)