Boiler Error Codes: What Your Boiler Is Telling You

The checks you can do first

Vaillant and Glow-worm both say a reset often clears a fault, and that you shouldn't open the boiler yourself. Before you press reset, it's worth ruling out the causes you can actually fix:

• Pressure. Look at the gauge on the front. Vaillant and Ideal both give 1 to 1.5 bar as the normal pressure. If it's below 1 bar, you can usually top it up through the filling loop, if your manual says you can.
• Gas. Check the hob or another gas appliance works, and that a pre-payment meter has credit. Ideal also suggests checking the yellow gas valve under the boiler is on (the handle in line with the pipe). If nothing on gas works, the problem is more likely the supply than the boiler, and Ideal says to contact a gas engineer.
• A frozen condensate pipe. In a cold snap, Vaillant and Glow-worm both list it as a reason the boiler won't light. More on that below.

Then reset it once. If the same code comes straight back, we'd stop there: pressing reset over and over won't fix a fault inside the boiler, and the code is what the engineer needs to know.

A frozen condensate pipe

A condensing boiler makes water, which runs to a drain through the condensate pipe: usually a white pipe, like a washing machine waste, coming out of the wall near the boiler. If the outside part freezes, the water backs up and the boiler stops. On a Glow-worm it shows as F28 or F29, Glow-worm says, and you may hear a bubbling or gurgling noise from the boiler.

• Find the frozen bit. It's usually the most exposed part: the end of the pipe by the drain, or a bend.
• Pour warm water along it from a jug or watering can until the ice clears. Never boiling water, which can damage the pipe.
• Reset the boiler the way its manual says.
• Lag the outside run with pipe insulation from a DIY store so it doesn't happen again.

If you're in any doubt, Glow-worm's advice is to contact your installer.

Vaillant fault codes

Vaillant boilers show an F followed by a number. These are the ones people look up most, from Vaillant's own list, with what it says you can check and who fixes the rest. Vaillant splits them between your installer and an engineer; either way, it's someone Gas Safe registered.

The ones you'll see most in autumn are F.22 (low pressure) and F.28 (the boiler didn't light, very often gas supply or a frozen condensate pipe).

Glow-worm fault codes

Glow-worm boilers use many of the same F codes, and Glow-worm's list gives the same meaning and advice as Vaillant's for the ones they share. The one most people search for is F28: the boiler has failed to light.

If the checks don't clear it, Glow-worm says not to try to solve it yourself, as opening the casing can be dangerous.

Ideal fault codes

On an Ideal, the code flashes as a letter and a number: F1 is F and 1, L2 is L and 2. These are the meanings on Ideal's fault code list.

F1 is low pressure, topped up through the filling loop. For F2 or L2, Ideal adds one more clue: if the boiler gurgles while it tries to light, contact your installer, as it may be a blockage. For most codes, Ideal's advice is to reset the boiler once and, if that doesn't fix it, call Ideal quoting the code.

Baxi error codes

Baxi publishes its codes on a page for installers. These are the meanings it gives for models including the Main Eco Compact, 600 and 800, Duo-tec, Assure, Platinum and EcoBlue (its newer Combi 2 and System 2 boilers use different codes). Baxi lists the meanings only; the checks are the same general ones as above.

Worcester Bosch symbols

Worcester Bosch boilers can show symbols on the display, and Worcester's own guide shows what each one means. One is worth knowing this time of year: siphon fill mode. After the boiler has been off, or hasn't been used for a day or so, it runs on a low flame for about 15 minutes to fill its condensate trap. That's a safety feature and perfectly normal. If it carries on for more than 30 minutes, Worcester asks you to ring them.

Some models also show a symbol, or the letters SE, when a service is due. That's a reminder, not a fault.

When to call someone, and who

If the checks haven't cleared it, write down the code and the boiler's make and model, so you can give them to the maker or the engineer.

• Still under warranty: we'd call the maker first, as Ideal suggests for its Logic boilers.
• Out of warranty: a Gas Safe registered engineer. See boiler repair costs.
• An old boiler with a run of faults: that's when it's worth pricing a new boiler alongside the repair.

Work inside a gas boiler must be done by a Gas Safe registered engineer: it's the law, not advice. Ask for their Gas Safe ID card: the back lists the kinds of gas work they're qualified for. See checking a gas engineer.

If the boiler's due a service anyway, we'd ask for both in one visit.

Frequently asked questions