BoilerFaultCodesYour boiler has stopped working because the electricity supply coming into your home is currently too weak to power the internal electronics safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Low 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.
DIY fix possible
Check if other appliances or lights in your home are flickering or dimmingSwitch the boiler off and back on at the fused spur switch to see if the error clearsContact your regional electricity distribution network operator (DNO) to report a local supply issue
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like F7 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
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.
Affiliate links — we may earn a commission at no extra cost to you.