Glow-worm F1 fault code — what it means and how to fix it

What does the Glow-worm F1 fault code mean?

The Glow-worm F1 fault code means the boiler has tried to light, failed after repeated ignition attempts, and locked out. The most common cause in cold weather is a frozen or blocked condensate pipe. Thaw the pipe, then reset the boiler. If F1 returns, book a Gas Safe registered engineer to investigate the gas supply or ignition.

In plain terms, F1 is an ignition lockout. After repeated failed attempts to establish a flame, the boiler stops rather than keep releasing gas — a safety response, not a fault to panic about. You'll see F1 on the digital display, and the display is also where the reset button sits. F1 can show up across many Glow-worm combi boilers, so check your model's manual for the exact wording, or call Glow-worm on 0330 100 3142.

On its own, F1 is not a gas emergency. It usually points to something simple — a frozen condensate pipe or an interrupted gas supply. The National Gas Emergency Service line, 0800 111 999, is only for when you can smell gas or your carbon monoxide alarm is sounding, not for this code.

Key facts

The quick version, before we get into the detail.

• What it means: ignition lockout after repeated failed ignition attempts.
• Most common cause: a frozen or blocked condensate pipe (a winter problem).
• DIY-fixable: partly — you can thaw the condensate pipe and reset; gas and ignition faults need an engineer.
• Affected models: seen across many Glow-worm combi boilers — check your manual for the exact wording.
• Smart Plan boiler cover: parts and labour up to £500 (boiler under 7 years) / £200 (over 7 years) per 12-month period. A bigger repair can exceed the £200 older-boiler limit, and you'd pay the difference.
• Minimum term: once you use a service, a 12-month agreement period begins. There's a 14-day cooling-off period that ends as soon as you use a service; leave early after that and 75% of the remaining term applies.
• Call-outs run Mon–Fri, 08:00–18:00, and a £95 call-out fee applies to each engineer visit under the plan.

Glow-worm F1 at a glance

Why does the Glow-worm F1 code appear?

F1 fires when the boiler can't establish a flame after several attempts. A handful of things stop that flame catching, and they're worth knowing so you can spot which one you're dealing with.

A frozen or blocked condensate pipe is the number-one cause in cold weather. When the pipe that carries waste water outside freezes, the water can't drain, and the boiler locks out. An interrupted gas supply is the next most common — including a prepay meter that's run out of credit, or a supply issue affecting the whole house. After that come faults inside the boiler: a worn or dirty ignition electrode or lead, or a failing gas valve. Those last two are engineer-only.

F1 is strongly seasonal. It spikes during cold snaps, precisely because frozen condensate pipes are behind so many cases. Glow-worm itself groups F1 with F4, F28 and F29 as codes that, in freezing weather, typically point back to a frozen condensate pipe — so a sudden F1 after a hard frost is a strong hint to check that pipe first.

What causes F1 and who can fix it

How to fix the Glow-worm F1 code yourself

In winter you can often clear F1 yourself by thawing a frozen condensate pipe and resetting the boiler. None of these steps involves opening the boiler or touching anything to do with gas — that's the line you never cross.

1. Find the condensate pipe. It's a plastic pipe — usually white — that runs from the boiler out through an external wall to a drain. In freezing weather it can ice up at the exposed bends, the open end, or any outdoor section.

2. Thaw the frozen section gently. Pour warm — never boiling — water along it, or hold a hot water bottle, a heat pack or a warm cloth against it. Boiling water can crack the plastic.

3. Check the gas supply. Make sure your other gas appliances work, that the gas is on, and — if you're on a prepay meter — that you've still got credit. An empty meter alone can trigger F1.

4. Reset the boiler. Press and hold the reset button on the digital display for a few seconds, then let go. The boiler will run through its ignition sequence and, if all's well, fire up.

Only reset once or twice. If F1 comes straight back, don't keep resetting — that won't clear a genuine ignition or gas-supply fault, and it can mask a real problem. Stop there and book a Gas Safe registered engineer. If the pipe keeps refreezing, ask an engineer to lag or reroute it so it doesn't happen every cold snap.

When to call a Gas Safe engineer for F1

Call an engineer if F1 persists after you've thawed the condensate pipe and checked the gas supply, or if the pipe clearly isn't frozen in the first place. That points to something inside the boiler — a worn ignition electrode, a failing gas valve, or a PCB (control board) fault — and each of those needs qualified diagnosis. Never open the casing: it's illegal for anyone who isn't Gas Safe registered to work on the gas side, and it isn't worth the risk. You can check an engineer is registered on the Gas Safe Register.

Repair costs depend entirely on the cause. A frozen-pipe thaw you do yourself costs nothing; an electrode is usually at the cheaper end; a gas valve or PCB is dearer. Ask your engineer for a quote before the work goes ahead.

Dealing with F1 right now?

If F1 is on your display today and the DIY checks haven't cleared it, the route is a one-off repair — a new cover plan won't cover a fault you're already having. Book a one-off repair and a Gas Safe registered engineer will come and fix it for you during call-out hours, Mon–Fri, 08:00–18:00. Call 0333 772 6247. F1 is a winter fault and lockouts often happen at night or at the weekend, so if it's outside those hours you may need to wait until the next working day for a visit.

Cover for the next time F1 appears

Smart Plan is a service plan, not insurance. It covers future faults, not one you're already dealing with, so it's for peace of mind next time rather than a fix for today's lockout. An ongoing boiler module covers parts and labour up to your cover limit — up to £500 a year if your boiler is under 7 years old, or up to £200 if it's older. Worth being clear-eyed about the older-boiler figure: a bigger job such as a gas valve or PCB can cost more than £200, and you'd pay the difference above the limit. Using a service starts a 12-month agreement period (there's a 14-day cooling-off window, which ends as soon as you use a service; leave early after that and 75% of the remaining term applies). A £95 call-out fee applies to each engineer visit, and call-outs run Mon–Fri, 08:00–18:00. Cover is modular, so you pick only what you want. UK Boiler Company Ltd, our parent company, has traded since 2014 and, by its own figures, has looked after over 15,000 customers.

Safe checks before you call anyone out

The only things worth trying yourself with an F1 fault. If none of them clear it, the next step is a Gas Safe registered engineer.

• Check your other gas appliances. If the hob won't light either, it's a gas supply issue, not the boiler.
• Make sure the gas is on — and if you're on a prepay meter, check you still have credit.
• In cold weather, check the external condensate pipe for ice and thaw it gently with warm — never boiling — water.
• Press reset on the digital display once, and try one more time if needed. Don't keep resetting if F1 comes back.
• Never open the casing or touch the electrodes, gas valve or wiring — that's gas work, and it's a Gas Safe registered engineer's job.
• If you ever smell gas or your CO alarm sounds, stop. Call the National Gas Emergency Service on 0800 111 999, open windows, turn off the gas at the meter, don't touch electrical switches, and leave the house.

Glow-worm F1 fault FAQs

Seeing F1? Here's how to get it sorted.

For an F1 fault right now, book a one-off repair and a Gas Safe registered engineer will fix it during call-out hours (Mon–Fri, 08:00–18:00). A Smart Plan boiler module is separate — it covers future faults, not one you already have, with parts and labour up to your cover limit. A service plan, not insurance.

Helpful links

• Glow-worm F9 fault code
• Glow-worm F22 fault code
• Boiler & central heating cover
• No heating? Book a repair
• All boiler fault codes
• Glow-worm boiler fault codes (official advice)
• Check an engineer on the Gas Safe Register