High
AL 81 on Sime Murelle One HE

Your boiler has detected a problem with how the gas is burning when it tries to start, likely caused by a blockage in the air or exhaust pipes.

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 One He installation & service manual, page 43.
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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