Glow-worm F.88 fault codewhat it means and how to fix it
The gas valve assembly is not connected, is connected wrongly, or its harness is shorted. The board found this on its self-check, so no gas has been released and nothing lights.
Take care
Get a Gas Safe registered engineer to look at your Glow-worm F.88
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.
What F.88 means
Glow-worm print F.88 as "Fault: Gas valve assembly" on the Energy7, Ultimate3, Easicom3, Betacom3 and 4 and Compact, with the causes "gas valve assembly not connected or it is connected incorrectly, short circuit in the wiring harness". It is the sibling of F.87 for the igniter and F.89 for the pump: the newest boards test each actuator is present and sane before every start, and F.88 is that test failing for the valve. It is not F.61 — that is a control fault found while the valve is being driven — and it is not F.62. Nothing is passing gas; the valve has not been asked to open, and the board will not ask it while the circuit reads wrong.
Practically, F.88 turns up in two situations. After a repair, where the valve plug has been left off or pushed on to the wrong header — and after years of service, where the harness has chafed through against the gas valve body or the casing.
A valve whose coil has gone open circuit shows the same signature, and Glow-worm's checks for the engineer run in that order: the connection, the harness, then the assembly. This is a current-range code only; the two-digit Ultracom2 and Betacom2 tables end at F86 and Err, and the older Ultracom lists at F77. Every Glow-worm user guide for the ranges that show it reserves it for a competent person, and there is nothing to be gained from a reset: the board repeats the same check and finds the same missing valve.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Valve plug off or on the wrong header | Glow-worm's first cause, usually after a service or a board change. The plug is a small keyed connector on the valve body and it is easy to leave unseated. | Common |
| Harness to the valve chafed or shorted | The loom runs past the gas valve body and the burner door, and a conductor worn through to earth trips the presence check. Glow-worm's second cause. | Occasional |
| Valve coil open circuit | The assembly itself has failed electrically. Reached last in Glow-worm's checklist, and replaced as a unit. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£400
Time on site
1 hour
Free if a plug was off. Harness repair £90–£150. Gas valve assembly £250–£400.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
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Glow-worm gas valve assembly
£90–£200Authorised Glow-worm parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
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
Common questions about Glow-worm F.88
Is this a gas leak?
No. The board has not opened the valve and will not while F.88 stands. If you can smell gas it is a separate matter for 0800 111 999, but this code does not itself mean gas is escaping.
F.61, F.62 or F.88 — what is the difference?
F.88 is the valve not found on the self-check. F.61 is the valve present but its control circuit faulty when driven. F.62 is the valve failing to shut off cleanly. Glow-worm print all three as separate rows.
Cost?
A reconnection is trivial. A harness repair £90–£150. A gas valve assembly £250–£400 fitted, and it is the last thing an engineer should change.
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
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.