Glow-worm F.67 fault codewhat it means and how to fix it
F.67 means the flame signal the board's ASIC reports is implausible — the electronics disagree with themselves about whether there is a flame. The Compact adds the flue route as a cause.
Take care
Get a Gas Safe registered engineer to look at your Glow-worm F.67
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.67 means
Glow-worm's title for F.67 on the Energy and Ultimate is a mouthful — "value sent back by ASIC is incorrect (flame signal)" — and its two causes are "implausible flame signal, electronics defective". The ASIC is the chip on the main board that monitors the ionisation current through the flame; F.67 is raised when what it reports cannot be reconciled with what the rest of the board expects, which is a different fault from F.27 (flame seen when there should be none) or F.68 (a real but unstable flame).
The Compact manual is more generous with causes: "implausible flame signal — check the flame signal", "PCB defective — replace the PCB", and then "fault in the flue gas route — check the entire flue gas route", because recirculating flue gas can disturb the ionisation current enough to make the signal nonsensical. The two-digit Ultracom2, Betacom 24a/28a and Betacom2 list F67 as "flame signal fault in the main board" with the shared F61-to-F67 measures — connections, board, DSN, reset. There is no 67 in the older Ultracom, Flexicom or CI tables.
An engineer checks the flame sensing electrode and its lead, and on a Compact the flue, before deciding the board is at fault; a poor earth on the boiler chassis is a known way to corrupt the ionisation reading and is cheaper to fix than anything on the board. Glow-worm give no householder step.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Flame sensing circuit giving an implausible reading | Glow-worm's first cause. The electrode, its lead or the boiler's earth connection produce an ionisation current the board cannot interpret. Checked and cleaned or corrected before the board is suspected. | Common |
| Flue gas recirculating — Compact | The Compact manual's third cause: a fault in the flue gas route. Products of combustion drawn back into the air intake disturb the flame and its signal. | Occasional |
| Main board ASIC failed | "Electronics defective." The flame monitoring chip itself; the board is replaced and configured with the correct Device Specific Number. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£100–£380
Time on site
1 hour
Electrode, lead or earth corrected £100–£180. A main PCB £250–£380 fitted.
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
Glow-worm main PCB
£150–£320Authorised Glow-worm parts distributor
Price checked 28 September 2026
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Related Glow-worm fault codes
- F.70Get it checkedF.70 means the boiler does not know which model it is — the Device Specific Number is missing, wrong or does not match the coding resistor, usually after a board or display has been changed.Related: electronics and communication
- F.49Get it checkedF.49 is an eBUS fault — the control bus voltage has dropped through a short, an overload or two supplies wired with opposite polarity. It points at the wiring to your controls.Related: electronics and communication
- F.63Get it checkedF.63 is an EEPROM fault — the memory on the main board has failed its check. Glow-worm give one cause, "electronics defective", and one measure, replace the PCB. Nothing else clears it.Related: electronics and communication
- F15Get it checkedF15 is the eBUS voltage on an Ultracom, Flexicom or Ultrapower, and the gas valve stepper motor on a cxi, CI or CI Plus. Know which boiler you have before anyone orders a part.Related: electronics and communication
- F.64Get it checkedF.64 is the board's analogue-to-digital converter reporting a reading it cannot make sense of — Glow-worm blame a shorted flow or return sensor first and the electronics second.Related: electronics and communication
- F12Get it checkedF12 on a cxi, sxi, CI or Xtramax is the link between the main board and the display board. F.12 on an Energy7 system boiler is a cylinder sensor short. Different generations, both engineer's codes.Related: electronics and communication
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.