BoilerFaultCodes 1621 Medium
Boiler Fault Code 1621
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 1621 appears across 1 boiler brand and 1 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 correctly blend the temperature of your hot water, which will likely result in your taps running cold or lukewarm. (As reported on Warmflow 70/90 Combi)
Pick your boiler brand for the 1621 fix
Source
Information for the 1621 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026