BoilerFaultCodes 18 High
Boiler Fault Code 18
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 18 appears across 21 boiler brands and 65 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's control panel and its main computer are having trouble communicating with each other, meaning you cannot change settings or see the boiler's status correctly. (As reported on Glow-worm 30ci Plus)
Pick your boiler brand for the 18 fix
Alpha 18 2 models Atag 18 1 model Baxi 18 3 models Biasi 18 4 models Chaffoteaux 18 6 models Ferroli 18 1 model Glow-worm 18 6 models Grant 18 1 model Heatline 18 1 model Ideal 18 5 models Main 18 1 model Malvern 18 1 model Potterton 18 1 model Remeha 18 1 model Saunier Duval 18 2 models Sime 18 2 models Unical 18 2 models Viessmann 18 17 models Vokera 18 4 models Warmworld 18 2 models Worcester Bosch 18 2 models
Source
Information for the 18 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