F7 Boiler Fault Code: What It Means on Every Brand

F7 is a mains-voltage fault on Ideal and Keston (the supply dropped below the minimum), a pressure-sensor fault on Glow-worm, and a 'false flame' ionisation fault on Worcester Bosch. If lights dimmed at the same time, the Ideal/Keston version is probably a supply blip; the Worcester version is never one to keep resetting.

Lockout — engineer likely 4 brands use this code

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What F7 means	Severity	DIY?
GWGlow-worm	The F7 fault code on Glow-Worm boilers signals that the boiler cannot confirm a change in water pressure after the pump starts up. Full guide →	Lockout — engineer likely	No
IIdeal	The F7 code on an Ideal boiler means the appliance has detected that the incoming mains voltage has dropped below approximately 190 volts. Full guide →	Lockout — engineer likely	No
KKeston	The F7 fault code on Keston boilers signals that the mains electrical supply reaching the boiler has dropped below the acceptable threshold — typically under 190V, against the required… Full guide →	Lockout — engineer likely	No
WBWorcester Bosch	The F7 fault code means your Worcester Bosch boiler's ionisation circuit has detected a flame signal at a point when the burner should be off. Full guide →	Lockout — engineer likely	No

F7 brand by brand

Glow-worm F7

The F7 fault code on Glow-Worm boilers signals that the boiler cannot confirm a change in water pressure after the pump starts up. When the boiler fires, it briefly runs the circulation pump and expects to detect a corresponding rise in system pressure — proof that water is moving safely around the system. If the pressure sensor fails to register that change, the boiler locks out and displays F7 as a safety precaution. On newer Glow-Worm models this same underlying fault appears as F75, which is simply a more precise variant of the same detection failure. Both codes point to the same root cause: the boiler cannot verify proper water circulation. The fault may stem from the pressure sensor itself, the circulation pump, or low system water pressure — each of which prevents the boiler from completing its start-up self-check.

Causes, fixes & costs for Glow-worm F7 → · All Glow-worm codes

Ideal F7

The F7 code on an Ideal boiler means the appliance has detected that the incoming mains voltage has dropped below approximately 190 volts. Although gas boilers burn fuel for heat, they rely on a steady electrical supply to power the control board, display, pump, fan, and ignition system. When that supply falls too low, the boiler shuts down as a safety precaution and locks out rather than risk unreliable or unsafe operation. Unlike most boiler faults, F7 originates in your home's electrical supply rather than inside the boiler itself, so the first port of call is often a qualified electrician rather than a Gas Safe engineer.

Causes, fixes & costs for Ideal F7 → · All Ideal codes

Keston F7

The F7 fault code on Keston boilers signals that the mains electrical supply reaching the boiler has dropped below the acceptable threshold — typically under 190V, against the required 230V ~ 50Hz supply. When voltage falls this low, the boiler's controls, pump, fan, and ignition circuitry cannot operate reliably, so the appliance locks out and displays F7 as a protective measure. Crucially, this fault originates in your home's electrical supply rather than inside the boiler itself, making it one of the few boiler fault codes where a qualified electrician — not a Gas Safe engineer — is usually the first professional you need to call. Keston is now part of the Ideal Heating group, and the F7 code carries the same meaning across both brands.

Causes, fixes & costs for Keston F7 → · All Keston codes

Worcester Bosch F7

The F7 fault code means your Worcester Bosch boiler's ionisation circuit has detected a flame signal at a point when the burner should be off. Because the control system believes a flame is present when none should exist, the boiler immediately locks out as a safety precaution and stops all heating and hot water until the underlying cause is identified and resolved. On some models — particularly those in the Greenstar Si range — the full display reads 'F7 228', which specifically indicates a false flame signal detected before ignition begins. Both 'F7' and 'F7 228' point to the same root problem: either a component is sending a rogue signal, or gas is reaching the burner when it should not be. This is a safety-critical fault; do not attempt repeated resets or try to override the lockout.

Causes, fixes & costs for Worcester Bosch F7 → · All Worcester Bosch codes

Frequently asked questions

Is the F7 fault code the same on every boiler?

Broadly, yes — on Glow-worm, Ideal, Keston and Worcester Bosch the F7 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a F7 fault myself?

Not usually. On every brand listed, F7 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a F7 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.