Boiler Fault Code Flow/Flue Thermistor Fault

Also written as FLOWFLUETHERMISTORFAULT — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code Flow/Flue Thermistor Fault appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has stopped working because it cannot correctly measure the temperature of the water flowing through it, likely due to a faulty sensor or a loose electrical connection. (As reported on Keston Heat 45)