How much does it cost to fix boiler error code Er 12?

Typical repair cost for the boiler Er 12 fault is £120-220 including labour.

Er 12 High

Boiler Fault Code Er 12

Also written as ER12 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code Er 12 appears across 4 boiler brands and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has stopped working because a sensor that measures the temperature of the water coming back into the system has developed a fault or is sending an incorrect signal. (As reported on Biasi Concept 400 20 1 Mfs)

Pick your boiler brand for the Er 12 fix

Biasi Er 12 3 models Ferroli Er 12 1 model Johnson Starley Er 12 1 model Vaillant Er 12 1 model

Source

Information for the Er 12 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