BoilerFaultCodes Block 86 High
Boiler Fault Code Block 86
Also written as BLOCK86 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Block 86 appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has detected that the electricity supply coming from your wall socket is unstable or outside of the standard frequency range, preventing it from operating safely. (As reported on Atag E32S)
Pick your boiler brand for the Block 86 fix
Source
Information for the Block 86 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 27 April 2026