BoilerFaultCodesPotterton THERMISTOR Fault Code
The Potterton THERMISTOR fault code means: your boiler has detected a faulty temperature sensor which means it can no longer accurately monitor how hot the water is getting.. It appears on 7 Potterton models in our database.
Technical description: Lights: On Flash On. Unplug thermistor, check if thermistor resistance is between 0.5kΩ & 20kΩ. Plug in thermistor, leave 8-way connector unplugged, check resistance at D between 0.5kΩ & 20kΩ.
What causes the Potterton THERMISTOR fault?
This fault occurs when the internal temperature sensor fails to send a reliable signal to the main control board, often due to internal corrosion or electrical fatigue. Because the boiler can no longer track how hot the water is, it shuts down as a safety precaution to prevent the system from overheating. In some cases, the problem can also be caused by loose or damaged wiring that has broken the connection between the sensor and the brain of the boiler.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Potterton models that show the THERMISTOR fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton THERMISTOR fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
- Potterton Promax HE manual (PDF)
- Potterton Promax FSB 30HE manual (PDF)
- Potterton Promax SL 24 Heat ErP manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026