Glow-worm F14 fault codewhat it means and how to fix it
F14 is two faults under one number: gas valve control on the Ultracom, Flexicom and Ultrapower, and flow temperature above 95 °C on the cxi, CI and Xtrafast. Engineer either way.
Take care
Get a Gas Safe registered engineer to look at your Glow-worm F14
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 boiler do you have?
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.
An Ultracom, Flexicom or Ultrapower — sold from about 2006, reset button on the fascia
Gas valve control defective. A gas fault.
Do not reset repeatedly. Book a Gas Safe registered engineer.
A cxi, sxi, SI, CI, CI Plus or Xtrafast — early 2000s, reset from the On/Off switch
Flow temperature above 95 °C — an overheat from poor circulation.
Let the boiler cool, 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 F14 means
Glow-worm's two older code lists both include F14 and do not agree about it. On the Ultracom cxi, hxi and sxi, the Flexicom cx, hx and sx and the Ultrapower, F14 is "gas valve control defective" — the board cannot drive the gas valve as it expects, the fault the current ranges report as F.61. On the earlier cxi, sxi, SI, CI and CI Plus it is "central heating flow temperature > 95 degrees", the 24CI/18SI manual lists 14 as "over temperature on primary water circuit", and the Xtrafast table has "central heating flow temperature > 97 degrees" — the fault the current ranges report as F.20.
One is a gas fault, the other a circulation fault, and they share nothing but the number. The way to tell them apart is the boiler: an Ultracom or Flexicom has the name on the front, was sold from about 2006, and has a reset button; a cxi, CI or Xtrafast dates from the early 2000s and is reset from the On/Off switch.
For the over-temperature version the user guides for the ranges concerned give nothing beyond a reset once the boiler has cooled, and the causes are those of any overheat — a pump slowing, a valve shut, air, low pressure — which the F.20 page covers. For the gas valve version there is nothing a householder may do at all: a gas valve that will not follow the board is a gas-carrying part and the boiler is right to stay off. Neither meaning appears on the two-digit Ultracom2 and Betacom boards or the current F.xx ranges under this number.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Gas valve control — Ultracom, Flexicom, Ultrapower | "Gas valve control defective." The valve's coils, its lead or the board's drive circuit; the engineer meters the valve and the harness before condemning the board. The current ranges' F.61 page describes the same fault in Glow-worm's later words. | Common |
| Flow above 95 °C — cxi, sxi, SI, CI, CI Plus, Xtrafast | Water not moving through the heat exchanger fast enough to carry the heat away: a pump slowing, a diverter valve stuck, air in the boiler or low pressure. The boiler stops before the overheat thermostat has to. | Common |
| Sensor reading high | On either list, a flow thermistor drifting high makes the board believe a temperature the water never reached. Less common than the real thing, and checked when the pump proves fine. | 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
An overheat traced to a pump or valve £80–£300. A gas valve on an Ultracom or Flexicom £250–£320 fitted, where still available.
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
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
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 support portal
- 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.