Emergency
AL 01 on Sime Ecomfort System Plus HE EV

Your boiler has detected that dangerous exhaust gases are not being cleared safely through the chimney, causing it to shut down to prevent carbon monoxide from entering your home.

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 Ecomfort Plus He Ev Combi installation & service manual, page 27.
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 03View →AL 05View →

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