Medium
AL 43 on Sime Murelle Pro HE Combi

Your boiler is having trouble communicating with your thermostat or smart controller, 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

Open Therm communication fault — check OpenTherm wiring/remote control connection

From this model's manual
Verified against the Sime Murelle Pro He Combi installation & service manual, page 32.
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 your thermostat or remote control has power or fresh batteries.Ensure all cables connecting the thermostat to the wall are plugged in securely.Restart the boiler by turning the power off and on again to reset the connection.

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Related fault codes

AL 42View →AL 06View →

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