Glow-worm F.63 fault codewhat it means and how to fix it
F.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.
Take care
Get a Gas Safe registered engineer to look at your Glow-worm F.63
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.63 means
The EEPROM is the small memory on the main board that holds the boiler's configuration and its settings between power cuts. F.63 on the Energy, Ultimate and Easicom is "Fault: EEPROM", and Glow-worm's cause list is one word long: "electronics defective". The Compact manual is equally brief — "PCB defective — replace the PCB".
On the two-digit Ultracom2, Betacom 24a/28a and Betacom2 the code is F63, "fault in the main board memory", and it is grouped with F61 to F67 under a shared set of measures: check the main board connections, check the main board, check the appliance DSN number is correct, reset the appliance. That shared list is the only reason to try anything short of a new board — a reset occasionally clears a one-off memory check failure after a power interruption, and Glow-worm's two-digit manuals allow it.
On the current ranges they do not, and a board that has genuinely lost its memory will fail the check again on the next power-up. The Ultracom hxi and Flexicom tables have F13, "PCB memory or sensing fault", which is the nearest older equivalent and points at the same part. There is no householder step for F.63 in any Glow-worm user guide; the code says the board can no longer trust its own settings, and only replacing it — and configuring the new one with the correct Device Specific Number — puts that right.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Main board memory failed | Glow-worm's one cause. The EEPROM has corrupted or worn out, and the board fails its self-check on power-up. Replaced as a board; the memory is not a serviceable part. | Common |
| Power interruption during a write | A supply cut at the moment the board was saving a setting can leave the memory inconsistent. The two-digit manuals' shared measure — reset the appliance — is aimed at this, and it is the only case in which F63 clears without a new board. | Occasional |
| Board damaged by a fault elsewhere | Water from a leak above, or a short on the harness, can take the board with it. The engineer finds the cause before fitting the replacement or the new one goes the same way. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£250–£380
Time on site
1 hour
A main PCB fitted and configured £250–£380 on most current ranges. There is no cheaper repair for a failed EEPROM.
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 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
- 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
- F.65Get it checkedF.65 means the main board itself has got too hot — from something outside it, Glow-worm say first, or because it is failing. The boiler stops to protect its electronics.Related: electronics and communication
Own a Glow-worm boiler? Save it and its codes come first next time.
Related guides
Common questions about Glow-worm F.63
Can I try switching it off and on?
On a two-digit Ultracom2 or Betacom, Glow-worm's own measures for F61 to F67 end with "reset the appliance", so one reset is within what the manual allows. On the current F.xx ranges the manual gives no such step. Either way, if the code returns, stop.
Why does a new board need a Device Specific Number?
Because the same board serves several models. The DSN tells it which one it is in; without it the boiler shows F.70 instead. Setting it is part of the engineer's job when the board is fitted.
Is F.63 dangerous?
No. The board stops the boiler rather than run on settings it cannot verify, which is the safe response.
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.