High Lockout
E.00 – .04 on Baxi 200 Combi (range)

Your boiler has detected a problem with the internal sensor that monitors water returning from your radiators, meaning it cannot safely regulate its temperature and has stopped working.

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

Return temperature sensor open-circuit. Sensor not or badly connected.

What causes this fault?

This fault occurs when the boiler's control system loses communication with the sensor that monitors water coming back from your radiators. The most common reason is that the sensor itself has developed an internal electrical failure or the wiring connecting it to the main control board has come loose or become damaged. Without this data, the boiler cannot accurately balance its heat output, so it shuts down as a safety precaution.

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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