Boiler Fault Code 1 8.

Also written as 18 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 1 8. appears across 2 boiler brands and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has shut down because the water inside has become too hot, usually due to a lack of circulation or a blockage. (As reported on Remeha Quinta Ace 25)