F7 on an Ideal boiler means low mains voltage. The appliance is not receiving a supply within the range it needs to run reliably.

This is one of the few codes where the manufacturer’s own answer is to contact the electricity provider rather than a heating engineer.

What F7 actually means

Boilers need a stable mains supply. Fans, pumps and ignition all depend on it, and running them on a low or unstable supply causes erratic behaviour and premature failure.

Rather than run badly, the boiler flags the supply and stops.

What you can safely check yourself

Check whether other things in the house are behaving oddly, lights dimming, other appliances tripping. If so the problem is the supply, not the boiler.

Check the boiler is not on an extension lead or a spur shared with something heavy. It should be on its own fused connection.

Ask the neighbours. If the street is affected, it is a distribution problem.

When to stop, and why

What causes it beyond the simple checks

A genuine supply problem from the network, an overloaded or poor quality circuit within the property, a loose connection at the fused spur or terminal block, or damaged wiring. Occasionally a boiler PCB misreading the supply, but the supply gets ruled out first because that is where the fault usually is.

How Vantage can help

We are Gas Safe registered under 956889 and cover Hertfordshire, Bedfordshire and Cambridgeshire, with an emergency line answered 24 hours a day. Call us on 01462 506374. See also boiler repair and boiler servicing.

Frequently asked questions

Should I call an electrician or a plumber for F7?

Start with the supply. If other appliances are affected too, it is electrical. If the boiler is the only thing complaining and the supply tests fine, then it comes back to the appliance.

Can low voltage damage my boiler?

Running fans and pumps on an inadequate supply is hard on them over time, which is part of why the boiler refuses rather than continuing.

Is F7 common?

Less common than the sensor and ignition codes, which is exactly why it gets misdiagnosed as a boiler fault.

Related fault codes

Other Ideal codes: L1 · L2 · LC · L6 · F1 · F2 · F3 · F4 · F5 · F6 · F8 · F9 · all boiler advice. See also boiler repair.

In Ideal’s own words

Ideal use different code sets across their ranges and generations. The definition above comes from The Ideal installation and servicing guide. If your boiler is a different model and the code behaves differently, check the manual for your appliance or ring us and we will tell you what it means on your unit.

When to call an engineer

If the checks above have not cleared it, the next steps are engineer work and the boiler should not be reset repeatedly in the meantime. Call Vantage Plumbing and Heating on 01462 506374. We are Gas Safe registered under 956889, the line is answered by a person at any hour of any day, and you get a price before anyone starts.

Need help today?

Call and speak to a person, any hour, any day of the year. Get a fixed price quote or call 01462 506374.