Vaillant F.67 fault codewhat it means and how to fix it
The 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.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.67
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What F.67 means
A Vaillant boiler proves its flame by measuring the tiny ionisation current that a flame conducts between the electrode and the burner. F.67 means the board is seeing a value for that current that cannot be right. The 2009 servicing instructions describe it exactly: "flame detector input signal is outside the limits (0 or 5 V) — electronics defective", meaning the input is pinned at one end of its range rather than reading a flame or no flame.
The ecoTEC plus and pro call it "electronics/flame — implausible flame signal" and have the engineer check the cable harness, the flame monitor and the PCB; the ecoFIT and ecoTEC sustain name the chip, "value sent back by ASIC is incorrect (flame signal)"; and the 2022 CS/1-5 says flatly "the flame monitor is defective", with the flame signal to be checked and the PCB replaced.
The distinction from its neighbours matters. F.27 is a flame detected when there should be none, F.28 and F.29 are a flame that would not light or went out, F.68 is a flame signal that is present but unstable. F.67 is the measuring circuit itself giving an answer outside anything physical. On the ecoMAX it is "electronic fault in flame system (non-plausible flame signal)" and on the turboMAX plus simply "electronic fault". It is not a row on the 2005 ecoTEC.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Flame monitoring circuit on the board failed | Vaillant's stated cause on every generation. The input stage that measures ionisation current has failed and reports a value outside its limits. | Common |
| Cable harness fault on the electrode lead | The ecoTEC plus check list starts with the harness. A shorted or open ionisation lead can pin the input at one end of its range. | Occasional |
| Moisture on the electronics | Condensation or a leak onto the board disturbs the very small currents the flame circuit reads. Dries out and returns, which is the pattern that points to it. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£90–£400
Time on site
1 hour
A harness repair or a dry-out is a call-out of £90 to £150. A replacement PCB is £250 to £400 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.
Vaillant main PCB (electronics box)
£160–£340Authorised Vaillant parts distributor
Price checked 28 September 2026
Vaillant wiring harness (plug-and-cable set to a sensor or actuator)
£20–£65Authorised 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.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.67
Is F.67 a gas safety problem?
It is the flame safety circuit reporting that it cannot be trusted, and the boiler has stopped for that reason. No gas is being burned. Do not keep resetting it; the circuit that would prove a flame is the one at fault.
Is it the electrode or the board?
Vaillant's tables point at the electronics, with the harness checked first on the ecoTEC plus. The electrode itself is more often behind F.68 or F.28. An engineer measures the lead before changing the board.
How much is a new board?
Typically £250 to £400 fitted for an ecoTEC. Check whether the boiler is still under Vaillant's guarantee before agreeing to it.
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.