High
d1 on Worcester Bosch Greenstar 25HE

Your boiler is struggling to monitor the temperature of the water returning to it, which is preventing the heating system from working correctly.

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

No return signal from LSM (Low Loss Header Sensor).

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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