Medium
EF 349 on Worcester Bosch Greenstar 30i

Your boiler is working harder than it should because water isn't moving through the system quickly enough to take away the heat.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.

Shared across the range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Check that all radiator valves are fully openEnsure the central heating system pressure is between 1 and 1.5 barBleed all radiators to remove trapped airCheck for any visible leaks around the pipework

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