High
On / Off on Worcester Bosch Greenstar 12i System

Your boiler is failing to communicate with your thermostat or timer, preventing it from turning on when it should.

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

Boiler not operating during central heating demand (HW ok) OR Boiler operating without live demand at ST10-LR(from external roomstat timer) OR Boiler not operating during hot water demand (CH ok) OR Boiler not operating during any demand.

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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