High Lockout
E44 on Keston C36

Your boiler has lost communication with the sensor that monitors water returning from your radiators, often causing the system to stop working as a safety 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

Return sensor open circuit – check connections to return sensor are in place

What causes this fault?

This fault occurs when the boiler's main control board can no longer read the temperature of the water coming back from your radiators. The most common reason is that the internal sensor has developed an electrical failure or the connecting wires have become loose or damaged. Because the boiler cannot monitor the water temperature accurately, it shuts down to prevent the system from overheating.

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

E43View →E05View →

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