BoilerFaultCodes 12 High
Boiler Fault Code 12
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 12 appears across 28 boiler brands and 129 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 4 models Atag 12 4 models Atmos 12 3 models Baxi 12 7 models Biasi 12 6 models Chaffoteaux 12 8 models Daikin 12 1 model Dimplex 12 3 models Ferroli 12 1 model Glow-worm 12 9 models Grant 12 5 models Heatline 12 1 model Ideal 12 6 models Intergas 12 7 models Johnson Starley 12 1 model Malvern 12 1 model Myson 12 1 model Potterton 12 3 models Ravenheat 12 7 models Remeha 12 2 models Saunier Duval 12 6 models Sime 12 2 models Unical 12 2 models Viessmann 12 3 models Vokera 12 6 models Warmworld 12 2 models Worcester Bosch 12 4 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 31 August 2026