High Lockout
E20 on Potterton Gold HE

Your boiler's internal temperature sensor has stopped sending a reliable signal, which means the system cannot safely monitor how hot the water is for your radiators.

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 NTC Fault

What causes this fault?

This fault occurs when the thermistor, a small sensor that monitors water temperature, fails or provides an incorrect electrical reading to the boiler's control board. The most common reason is internal degradation over time or loose wiring connections, which prevents the boiler from knowing when to safely turn the burner on or off.

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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