Vaillant F.97 fault codewhat it means and how to fix it
Vaillant'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.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.97
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.97 means
Most Vaillant codes have a check list. F.97 has a sentence. The ecoFIT pure and sustain, the ecoTEC sustain, the open-vent ecoTEC plus and the 48–64 kW plus all print "main PCB self-test failed — main PCB defective", and the 48–64 kW table and the 2022 CS/1-5 add the only instruction there is: "replace the PCB".
At every power-up, and again while running, the PCB tests the circuits it depends on for safety, and F.97 means one of those tests did not pass. Since the flame-proving and gas-valve circuits are among them, a board that has failed its test will not run, and no setting or reset overrides that.
What a householder can usefully know is what F.97 is not. It is not the display losing contact with the board — that is "con" on the two-digit ranges and F.707 on the CS/1-5, and it can look similar because both leave the boiler dead. It is not the electronics overheating, which is F.65 and clears when the board cools. F.97 is the PCB declaring itself unfit. The row is not printed on the ecoTEC plus ..6/5-5, pro or exclusive tables, and not on any legacy range.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Main PCB defective | Vaillant's only cause. A component in the board's safety circuits has failed and the self-test detects it. | Common |
| Water or condensation on the board | A leak from above onto the electronics box is the commonest way a good board becomes a failed one. An engineer looks for the source before fitting the replacement. | Occasional |
| Mains disturbance | A surge or a prolonged brown-out can damage the board. Vaillant do not list it for F.97; it is the usual history behind a board that fails without a leak. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£250–£400
Time on site
1 hour
A replacement PCB is £250 to £400 fitted. If a leak caused it, the leak is a separate repair.
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.63Get it checkedVaillant reports an EEPROM error, meaning the boiler cannot reliably read its own stored settings. The printed circuit board is at fault and needs replacing.Related: electronics and power
- 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.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.97
Is there anything to try before calling?
Switching the boiler off at its isolator for a minute and back on lets the board run its self-test again. If F.97 returns, Vaillant's remedy is a new board and nothing short of it will clear the code.
How much is a new board?
Typically £250 to £400 fitted for an ecoFIT or ecoTEC sustain. Check whether the boiler is inside Vaillant's guarantee first; the board is the part most worth claiming.
Is F.97 the same as "con"?
No. "con" is the display unable to talk to a board that may be working. F.97 is the board itself reporting a failed self-test. Both need an engineer, but F.97 nearly always means a board.
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.