High
d3 on Worcester Bosch Greenstar 28CDi

Your boiler is failing to detect a request for heat from your thermostat or internal timer, likely due to a loose wire or a disconnected control link.

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

Jumper 8-9 missing or heat demand external controller (ST8).

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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