Medium
AL 43 on Sime Murelle Pro HE MkII Combi

Your boiler has lost its connection with the smart thermostat or remote control system, meaning they can no longer talk to each other to manage your heating.

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 wall-mounted thermostat or remote control has power and fresh batteries.Inspect any visible wires between the thermostat and the boiler for signs of damage or loose connections.Turn the boiler power off at the fused spur switch, wait 30 seconds, and turn it back on to reset the communication link.

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AL 42View →AL 02View →

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