12 High

Boiler Fault Code 12

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code 12 appears across 32 boiler brands and 161 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is having trouble communicating with its control screen or your thermostat, which is preventing it from receiving your heating instructions. (As reported on Glow-worm Ci Plus)

Pick your boiler brand for the 12 fix

Alpha 12 24 models Ariston 12 6 models Atag 12 6 models Atmos 12 4 models Baxi 12 10 models Biasi 12 6 models Chaffoteaux 12 8 models Daikin 12 3 models Dimplex 12 2 models Ferroli 12 4 models Firebird 12 1 model Gledhill 12 1 model Glow-worm 12 11 models Grant 12 10 models Halstead 12 5 models Heatline 12 3 models Ideal 12 6 models Intergas 12 11 models Johnson Starley 12 1 model Malvern 12 1 model Maxol 12 1 model Myson 12 1 model Potterton 12 3 models Ravenheat 12 7 models Remeha 12 2 models Saunier Duval 12 9 models Sime 12 1 model Unical 12 2 models Vaillant 12 2 models Vokera 12 6 models Warmworld 12 1 model Worcester Bosch 12 3 models

Source

Information for the 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