Medium
4 green flashes on Baxi 400 Heat

Your boiler is having trouble communicating with the external controls or its internal components, meaning it might not know when to turn on or off.

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

Communication Fault warning

From this model's manual
Verified against the P3 Baxi 400 Heat installation & service 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 if your thermostat or programmer has power or fresh batteries.Ensure your thermostat is set to a temperature higher than the current room temperature.Reset the boiler by turning the selector switch to the 'R' position for at least five seconds.

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