High
AL 81 on Sime Murelle Pro HE System R

Your boiler has detected an issue with the air or gas mixture during ignition, often caused by a blocked chimney or an internal sensor problem, and has shut down for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Lockout due to combustion during start-up (blockage) — check flue for blockage; inspect air diaphragm (BF models); verify gas calibration

From this model's manual
Verified against the Sime Murelle Pro He System R installation & service manual, page 33.
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 high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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