High Lockout
E20 on Potterton Promax HE

Your boiler has lost its ability to measure the temperature of the water used for your radiators, causing the system to stop working for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Central heating thermistor sensor fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring the heat of the water leaving your boiler has failed or is sending an incorrect signal. The most common reason is that the internal component has simply worn out over time, though it can also be caused by loose or damaged electrical connections between the sensor and the main control board.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

E28View →E50View →E110View →

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