BoilerFaultCodesYour boiler has detected that the electricity supply from the mains is either too high or too low for it to operate safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Mains High Voltage or Low Voltage Error
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the incoming electrical power is outside the safe operating range of 230 volts. The most common reason is a fluctuation or surge in the local power grid, or a failing component on the control board misreading the incoming voltage.
This fault is more common during severe winter storms, as falling branches or high winds can cause power surges and fluctuations in the local electrical grid.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like H7 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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