BoilerFaultCodes Tank Thermistor not in Tank Medium
Boiler Fault Code Tank Thermistor not in Tank
Also written as TANKTHERMISTORNOTINTANK — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Tank Thermistor not in Tank 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 lost the connection to the temperature sensor inside your hot water tank, meaning it cannot accurately tell when the water is hot enough. (As reported on Potterton Promax HE Store)
Pick your boiler brand for the Tank Thermistor not in Tank fix
Source
Information for the Tank Thermistor not in Tank 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