Glow-worm F26 fault codewhat it means and how to fix it
F26 on a two-digit Ultracom2, Betacom 24a/28a or Betacom2 is the gas valve motor — disconnected or defective cables. On an early cxi, F26 is poor circulation. Engineer either way.
Take care
Get a Gas Safe registered engineer to look at your Glow-worm F26
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
Which display are you looking at?
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.
F26 without a stop on an Ultracom2, Betacom 24a/28a or Betacom2
Gas valve motor — its cables or the valve. A gas fault.
Do not reset repeatedly. Book a Gas Safe registered engineer.
F26 on an early-2000s cxi with a flashing red light
Poor circulation — the water side, not the gas.
Check the pressure gauge and that radiator valves are open, reset once from the On/Off switch, and book an engineer if it returns.
What F26 means
On the two-digit boards — Ultracom2 cxi and sxi, Betacom 24a and 28a, Betacom2 — Glow-worm's installation manuals give F26 as "fault in gas valve motor — disconnected or defective cables", with three measures: check the gas valve connections, check the operation of the gas valve, and check the operation of the condensate pump if one is fitted. The Ultracom2 trade table shortens it to "fault in gas valve". It shares its cause list with F77 on the same boards, and an engineer treats the two together: a gas valve whose motor the board cannot drive, or cannot hear back from, is replaced as an assembly, and a lead pulled during a service is put back.
On the early-2000s cxi the trade table has F26 as "poor circulation", the twin of its F25 — water not moving through the heat exchanger, the fault covered on the F.23 and F.24 pages — which has nothing to do with gas.
The Ultracom, Flexicom and Ultrapower have no F26. Among the current F.xx ranges only the Energy 35 Store lists F.26 — "Fault: gas valve without function", the stepper motor not connected, a plug on the PCB not home, a break in the harness or the motor itself defective — and it is the same part seen from the same side; the Energy, Ultimate, Easicom, Betacom3/4 and Compact report their gas valve through F.61, F.62 and F.88 instead, so an owner of one of those seeing what looks like F.26 should read the display again. The gas valve version has no householder step in any Glow-worm guide and should not have: a valve that does not answer its board is a gas-carrying part, and the boiler staying off is the correct outcome until an engineer has proved it.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Gas valve lead disconnected or damaged — two-digit boards | Glow-worm's stated cause: "disconnected or defective cables". A plug knocked off the valve during a service, or a lead chafed on the casing, and the board cannot drive the motor. | Common |
| Poor circulation — early cxi | On that one range F26 is the water side: pump, diverter valve, air or low pressure. The checks are those for F.23 and F.24. | Common |
| Gas valve motor failed — two-digit boards | The measure "check the operation of the gas valve". A motor that no longer moves the valve is replaced with the valve as one assembly; it is not serviced. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£320
Time on site
1 hour
A lead reconnected £80–£130. A gas valve assembly on a two-digit board £250–£320 fitted. A circulation fault on a cxi £80–£300 depending on the part.
Typical UK prices including parts and labour, updated September 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.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 28 September 2026
Glow-worm gas valve assembly
£90–£200Authorised Glow-worm parts distributor
Price checked 28 September 2026
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Related Glow-worm fault codes
- F.28Get it checkedThree ignition attempts have failed and the boiler has locked out. Glow-worm's guides let you check the gas supply and the condensate pipe and reset three times before calling anyone.Related: ignition and gas supply
- F1Get it checkedOn Ultracom, Flexicom and Ultrapower boilers F1 is an ignition lockout after five failed attempts, and Glow-worm's guides let you reset it. On Energy and Ultimate boilers F.01 is the return sensor instead.Related: ignition and gas supply
- F.29Get it checkedThe burner lit and then the flame went out while running. Glow-worm blame the gas supply, flue gas recirculating, earthing, the spark transformer and, on newer manuals, a blocked condensate pipe.Related: ignition and gas supply
- F.61Get it checkedThe board cannot drive the gas valve properly — a short in its wiring, coils shorted to earth, or the electronics. The valve stays shut until an engineer has traced it.Related: ignition and gas supply
- F.27Stop — call an engineerThe boiler is sensing a flame when there should not be one. Glow-worm list moisture on the electronics, a failed flame monitor or a leaking gas valve. Not a reset job.Related: ignition and gas supply
- F.68Get it checkedThe flame is burning but its signal is unstable. Glow-worm list air in the gas, low gas pressure, a wrong combustion setting or injector, a poor electrode connection or a blocked condensate pipe.Related: ignition and gas supply
Own a Glow-worm boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
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
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.