Vaillant F.63 fault codewhat it means and how to fix it
Vaillant reports an EEPROM error, meaning the boiler cannot reliably read its own stored settings. The printed circuit board is at fault and needs replacing.
Take care
Get a Gas Safe registered engineer to look at your Vaillant 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.
How old is the boiler?
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.
Still inside its manufacturer warranty
This should cost you nothing. Vaillant warranties are long by industry standards and a board is exactly what they exist to cover.
Contact Vaillant directly rather than an independent engineer, and have your installation date and serial number ready.
Out of warranty but under about twelve years old
A board is normally worth fitting at this age. ecoTEC units routinely run beyond fifteen years and the rest of the appliance likely has plenty left.
Get a written price for a board fitted before agreeing to anything.
Fifteen years old or more
Now it is an economic decision rather than a technical one. A board approaching £500 on an appliance near the end of its life is money towards a new one.
Ask the engineer to assess the heat exchanger and diverter valve at the same time so you can judge the whole picture.
What F.63 means
F.63 is an EEPROM error. EEPROM is the small area of memory on the circuit board that holds the settings the boiler needs to keep between power cycles — its configuration, its calibration, the parameters an engineer may have adjusted at commissioning. When the board can no longer read that memory dependably it raises F.63 and stops, because operating on settings it cannot trust would mean guessing at its own configuration.
Unlike most Vaillant codes this one has essentially a single answer. There is no sensor to test, no valve to clean and no wiring to reseat: the memory is part of the board and cannot be repaired separately, so Vaillant documentation points straight at defective electronics. That makes F.63 unusually simple to diagnose and unusually expensive to resolve, and it turns the real question into whether the boiler is worth the board.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Failed memory on the circuit board | The stored parameters can no longer be read back reliably, and the memory is not separable from the board. | Common |
| Board damaged by moisture | A leak from pipework above, or condensate escaping its trap, corrodes tracks and can present as a memory fault. | Occasional |
| Damage from an electrical surge | A nearby lightning strike or a supply fault can corrupt stored memory while leaving the rest of the board working. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£300–£550
Circuit board £300 to £480 fitted, including configuration for the appliance. Nothing at all if the boiler remains within its Vaillant warranty.
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.
Vaillant main PCB (electronics box)
£160–£340Authorised Vaillant parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Vaillant fault codes
- F.70Get it checkedThe boiler does not know which model it is. The device specific number is missing or wrong, which nearly always follows a board or display replacement.Related: electronics and power
- F.64Get it checkedAn electronics or sensor fault: the board cannot make sense of a safety-relevant sensor signal. Vaillant's causes are a shorted flow or return sensor or a defective board.Related: electronics and power
- F.65Get it checkedThe electronics have got too hot. Vaillant say either something outside the boiler is heating the board, or the board itself is faulty; the boiler stops until it cools.Related: electronics and power
- F.67Get it checkedThe flame signal the board is receiving is not believable. Vaillant treat F.67 as an electronics fault in the flame-monitoring circuit rather than a real flame problem.Related: electronics and power
- F.97Get it checkedVaillant's main PCB has failed the check it runs on itself. The table gives one cause, "main PCB defective", and one remedy: replace the PCB.Related: electronics and power
- F.195Get it checkedA 2022 ecoTEC plus code: the boiler has measured a significant undervoltage in its mains supply. F.196 is the overvoltage twin. Vaillant's first instruction is to check the mains, not the boiler.Related: electronics and power
Own a Vaillant boiler? Save it and its codes come first next time.
Related guides
Common questions about Vaillant F.63
What is EEPROM in plain terms?
Memory that survives being switched off. It holds the settings your boiler must remember — how it was configured at commissioning and any adjustments made since. When that memory becomes unreadable the boiler no longer knows how it is meant to behave.
Can the board be repaired instead of replaced?
Specialist firms do refurbish boiler boards, and it can be cheaper. Weigh it carefully: a refurbished board rarely carries the same warranty, and on a gas appliance the engineer fitting it is the person taking responsibility for it working correctly.
Will resetting help?
Not with this one. A reset asks the boiler to try again using the same unreadable memory, so the outcome is identical. One attempt to confirm the code is persistent is reasonable; beyond that there is nothing to gain.
Does a new board need setting up afterwards?
Yes, and it matters. A replacement board has to be configured for your specific appliance and system. Skipping that step is what produces a boiler that runs but never quite performs properly, and on some models it produces F.70 instead.
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.