BoilerFaultCodes 18 High
Boiler Fault Code 18
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 18 appears across 23 boiler brands and 78 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 3 models Atag 18 3 models Baxi 18 3 models Biasi 18 4 models Chaffoteaux 18 5 models Ferroli 18 4 models Firebird 18 1 model Gledhill 18 1 model Glow-worm 18 7 models Grant 18 6 models Heatline 18 3 models Ideal 18 7 models Main 18 1 model Malvern 18 1 model Potterton 18 1 model Remeha 18 3 models Saunier Duval 18 4 models Sime 18 1 model Unical 18 2 models Viessmann 18 12 models Vokera 18 2 models Warmworld 18 1 model Worcester Bosch 18 3 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 7 July 2026