Emergency
12 on Sime Murelle Advanced HE MkII Combi

Your boiler's computer system is confused about whether it is drawing air from inside your home or outside, so it has safely shut down to prevent any combustion risks.

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

Incorrect configuration of the open / sealed chamber

From this model's manual
Verified against the Sime/Sime Murelle Advanced He Mkii Combi 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

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All 52 fault codes on the Murelle Advanced HE MkII Combi

Seeing a different code? Every code this model can display, in one place.

02030405060708091011131415182837404142436272818396ALL 02ALL 03ALL 04ALL 05ALL 06ALL 07ALL 08ALL 09ALL 10ALL 11ALL 12ALL 13ALL 14ALL 15ALL 18ALL 28ALL 37ALL 40ALL 41ALL 42ALL 43ALL 62ALL 72ALL 81ALL 83ALL 96

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