Emergency
AL 03 on Sime Murelle Pro HE 25 HO

Your boiler has detected that there is too much water pressure in the system, which can cause the safety valve to leak or the unit to stop working.

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

High water pressure in system — drain via hydraulic assembly to ~1.2 bar

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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