Boiler Fault Code H9/L9

Also written as H9L9 — same fault.

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

Fault code H9/L9 appears across 1 boiler brand and 7 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 gases venting out of your home are getting too hot, so it has safely shut itself down to prevent damage or safety issues. (As reported on Ideal Mexico HE)