High Lockout
E20 on Baxi 600 Combi (range)

Your boiler's internal temperature sensor has developed a fault, meaning the system cannot correctly monitor the heat of your radiators and has shut down as a precaution.

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 negative temperature coefficient (NTC) thermostat fault.

What causes this fault?

This fault occurs when the sensor responsible for monitoring the water temperature in your radiators stops sending a reliable signal to the boiler's control board. The most common reason is that the sensor has physically burnt out or degraded over time, though loose or corroded wiring connections can also disrupt the electrical circuit.

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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