Glow-worm F.87 fault codewhat it means and how to fix it
The ignition electrode or igniter is not connected, is connected wrongly, or its harness is shorted. A wiring code rather than a worn-part code, and an engineer's job on every range.
Take care
Get a Gas Safe registered engineer to look at your Glow-worm F.87
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.87 means
F.87 is one of the codes Glow-worm added at the end of the table on the current ranges — the Ultimate3 manual prints it as "Fault: Ignition electrode", the Energy7 as "Fault: Electrodes" and the Compact as "Fault: Igniter" — and all three give the same causes: not connected, connected incorrectly, or a short circuit in the wiring harness.
Unlike F.28, which is a spark that did not light gas, F.87 is the board finding on its self-check that the igniter circuit is not there at all or is shorted, so it never gets as far as trying. That is why it appears most often just after a service or a repair: a plug left off the ignition transformer, a lead swapped, a harness trapped under the casing. It can also mean the igniter itself has failed open, in which case Glow-worm's checks lead the engineer from the connection to the harness to the part.
The two-digit Ultracom2 and Betacom2 tables stop at F86 and Err, and the Ultracom, Flexicom and Ultrapower lists end at F77, so F.87 is a current-range code only; if an older boiler seems to show it, read the display again. Glow-worm's operating instructions for the Energy7, Ultimate3, Betacom4 and Compact hand every code other than F.22, F.28 and F.83 to a competent person, and the igniter sits behind the sealed combustion cover, so there is nothing here for the householder to check.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Igniter or electrode plug left off or wrong | Glow-worm's first two causes, and the usual story when F.87 appears straight after an engineer has been. A five-minute fix for whoever comes back. | Common |
| Harness shorted | The ignition lead or its low-voltage side chafed through to earth or to a neighbour in the loom. Glow-worm's third cause and the one that takes the engineer longest to find. | Occasional |
| Igniter unit failed | The transformer or integrated igniter open circuit. Glow-worm's Compact checklist reaches it after the connections and harness are proved. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£180
Time on site
45 minutes
Free if a plug was left off after a service. Electrode or igniter £90–£180.
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.
Glow-worm ignition and flame-sensing electrode
£18–£45Authorised 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.87
It appeared the day after a service. Coincidence?
Probably not. Glow-worm's causes are all about connection, and a plug left off during a service is the most common way to earn this code. Call the same engineer back first.
Will the boiler try to light?
No. F.87 is found before ignition on the board's self-check, so there is no spark and no gas released — which is why it is caution rather than danger.
What does it cost?
A reconnection is often free under the service that caused it. An electrode or igniter fitted is £90–£180; a harness repair similar.
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.