High
345 on Worcester Bosch 24/28/35 CDi MkII

Your boiler is failing to detect any heat moving through the system after it ignites, usually because the pump isn't circulating water or a valve is blocked.

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.

What the manual says

Manufacturer manual

EF Supply and/or return temperatures do not change after burner start

From this model's manual
Verified against the Worcester Bosch Greenstar Cdi Compact installation & service manual, page 66.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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