E99 High

Boiler Fault Code E99

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code E99 appears across 3 boiler brands and 19 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 an electrical fault with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety. (As reported on Keston C36)

Pick your boiler brand for the E99 fix

Ariston E99 4 models Biasi E99 6 models Keston E99 9 models

Source

Information for the E99 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