BoilerFaultCodesWhat the manual says
Manufacturer manualLow mains voltage – contact electricity provider.
What causes this fault?
This fault occurs when the electrical voltage reaching the boiler drops below the minimum level required for its sensitive electronic components to function. While it can occasionally be caused by a failing internal control board, it is most often the result of an external issue with the local power grid or a temporary 'brownout' in your area. The boiler shuts down as a safety precaution because it cannot guarantee the correct operation of the gas valve and fan at such low power levels.
This fault is slightly more common during winter or extreme hot spells when the national grid is under heavy load, leading to a temporary drop in local supply voltage.
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.
Avoid the next call-out bill
A cover plan would handle faults like F7: no call-out fees, no surprise bills.
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