Emergency
AL 01 on Sime Murelle Pro HE 25 HO

Your boiler has detected that the exhaust gases are getting too hot or are not escaping correctly, causing the system to shut down for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

What the manual says

Manufacturer manual

Smoke thermostat (flue gas thermostat) intervention — open-flue variants only

From this model's manual
Verified against the Sime Murelle Pro He 25 Ho 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.

Engineer required

This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

AL 02View →AL 06View →AL 08View →

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