BoilerFaultCodesWhat the manual says
Manufacturer manualGas safety value failure
From this model's manual
Verified against the Glow Worm Cxi Csi System installation & service manual, page 37.
What causes this fault?
This fault occurs when the boiler's control board detects that the internal gas valve is not opening or closing correctly, or is drawing an incorrect electrical current. The most common reason is an electromechanical failure within the valve itself, though it can also be caused by a faulty circuit board sending the wrong signals to the gas assembly.
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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