Glow-worm F1 fault codewhat it means and how to fix it
No flame was detected during ignition, so the boiler has shut the gas off and locked out. Two resets at most before calling someone.
Stop — this needs an engineer
Get a Gas Safe registered engineer to look at your Glow-worm F1
Gas Safe Register engineers only. No obligation.
What else in the house runs on gas, and how cold is it?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
The hob will not light either
No gas at the property. Nothing wrong with the boiler.
Check the meter valve and prepayment credit, then call your supplier.
It is freezing outside
A frozen condensate pipe is the likeliest explanation.
Thaw the external white plastic pipe with warm, not boiling, water and reset once.
Gas is fine elsewhere and it is mild out
The fault is inside the appliance, most likely the electrode.
Book a Gas Safe registered engineer.
You can smell gas
Stop and treat it as an emergency.
Leave the property and call 0800 111 999 from outside.
What F1 means
F1 on a Glow-worm is a flame detection failure. The boiler completes its ignition sequence and then checks for an ionisation current across the sensing electrode to confirm gas is burning. Without that confirmation it closes the gas valve and locks out, because continuing to attempt ignition means continuing to release gas into a chamber where it is not burning. The usual causes are unglamorous: no gas reaching the appliance, an electrode that has carboned up, or a condensate pipe frozen solid. It is worth checking whether other gas appliances in the house still work before assuming the boiler is at fault.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| No gas at the appliance | Prepayment meter out of credit, a closed service valve, or a supply interruption. | Common |
| Worn ignition or flame sensing electrode | Carbon deposits stop the electrode detecting the flame it has lit. | Common |
| Frozen condensate pipe | Seasonal, and by far the easiest thing for a householder to rule in or out. | Common |
| Gas valve fault | Either failing to open or not delivering a stable enough rate to hold a flame through the ignition window. The dearest possibility on a Vitodens and the least frequent. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£120–£450
Time on site
1h 15m
Electrode £120–£200. Gas valve £280–£450. Condensate re-route £120–£250.
Typical UK prices including parts and labour, updated August 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Condensate trap and siphon
COND-TRAP£15–£38Plumbing merchant
Price checked 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Glow-worm fault codes
- F.28Get it checkedIgnition was unsuccessful at start-up and the boiler has locked out. Check the gas and the condensate pipe before calling anyone.Related: ignition and gas supply
- F.29Get it checkedThe flame was established and then lost, and re-ignition failed. Different from F.28 and it points somewhere else.Related: ignition and gas supply
- F.61Get it checkedA fault in the gas valve control circuit on the main board. The appliance will not fire and this needs an engineer.Related: ignition and gas supply
- EA 227Stop — call an engineerThe boiler tried to light and never detected a flame, so it has shut the gas off and locked out. This is the most common Worcester fault code.Related: ignition and gas supply
- E01Get it checkedThe appliance tried to light and could not confirm a flame, so it has locked out. In winter a frozen condensate pipe is the most likely reason.Related: ignition and gas supply
- F.28Stop — call an engineerThe boiler tried to light and failed three times in a row, so it has shut the gas off and locked out. Do not keep resetting it.Related: ignition and gas supply
Related guides
Common questions about Glow-worm F1
Why does it only fail first thing in the morning?
That pattern usually means condensate or a marginal electrode. Overnight the pipe is coldest and the appliance has been standing, so a fault that is borderline the rest of the day shows itself then. It is a fault getting worse, not a quirk.
How many resets before I stop?
Two. Each one triggers another set of ignition attempts with gas released each time. If two have not cleared it, the cause is real.
What will it cost?
An electrode is £120 to £200 fitted. A gas valve is £280 to £450. A frozen condensate is free if you can reach the pipe, or £120 to £250 to insulate and re-route so it does not happen again.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Trade body guidance
Checked by Technical reviewer (Gas Safe registration to be displayed on appointment) on 5 August 2026.