High Lockout
PP1 on Grant Vortex

Your boiler has stopped working because it cannot correctly measure the temperature of the water returning to the unit.

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

Inlet (return) water temperature sensor failure

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water coming back from your radiators. The most common reason is that the internal components of the sensor have failed or the electrical connection has become loose or corroded. Because the boiler cannot safely monitor the water temperature, it shuts down to prevent potential 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

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