Medium
AL 43 on Sime Murelle Pro HE R MkII System

Your boiler is having trouble 'talking' to your thermostat or external controls, which means 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 R Mkii System installation & service manual, page 40.
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 thermostat is powered on and has fresh batteries if applicable.Ensure any external control cables are securely plugged in and haven't been accidentally tugged or damaged.Try resetting the boiler by turning the selector knob to the 'R' position for a few seconds.

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Related fault codes

AL 42View →AL 06View →

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