Vaillant F.92 fault codewhat it means and how to fix it
The gas type the boiler has been told about does not match the coding resistor on its board. A commissioning or conversion fault; the boiler will not run on a gas it cannot confirm.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.92
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.92 means
F.92 is a second gas-type check, distinct from F.42. Where F.42 is the coding resistor itself failing, F.92 is the resistor reading correctly and disagreeing with a setting: the ecoTEC plus ..6/5-5 prints "fault: incorrect gas type — the coding resistor on the PCB does not match the gas group that is entered", and tells the engineer to check the coding resistor, carry out the gas family check again and enter the correct gas group. It appears when a boiler is converted between natural gas and LPG, when a board is replaced, or when the gas family check that is part of commissioning is answered wrongly.
On the 2022 CS/1-5 the code survives as F.092 with a narrower meaning, "the gas-type conversion was not completed correctly — gas conversion in D.156 not completed; check the setting in D.156", which is the same idea expressed for a boiler whose gas type is a setting rather than a resistor swap.
F.92 is only on the ..6/5-5 plus and the CS/1-5; the pro, exclusive, ecoFIT and ecoTEC sustain tables do not carry it. There is nothing here for a householder to do — every item is in the installer level — and it is a fault that the boiler is right to hold: a burner set for one gas and fed another is exactly what the check exists to prevent.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Conversion done without the matching setting | The boiler was converted to LPG or back to natural gas and the gas group entered during the gas family check does not match the resistor fitted. The commonest trigger by far. | Common |
| Board replaced with the wrong coding | A new PCB whose resistor or stored gas group differs from the boiler it went into. Vaillant's check is to repeat the gas family check. | Occasional |
| D.156 conversion not completed on a CS/1-5 | The three-digit boiler's own version: the conversion procedure under D.156 was started and not finished, and the board refuses to run until it is. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£120
Time on site
30 minutes
Completing the gas family check is a short visit, £80 to £120, and should be free if a recent conversion or commissioning caused it. No parts are normally involved.
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.62Stop — call an engineerThe gas valve is not shutting off when the boiler tells it to. This is a gas safety fault and the boiler must not be used until an engineer has seen it.Related: gas valve and supply
- F.61Get it checkedThe gas valve control circuit has faulted. The boiler will not fire and this is firmly an engineer's job.Related: gas valve and supply
- F.53Get it checkedThe gas is not flowing through the valve the way the boiler expects. Vaillant's list runs from low gas pressure to a wet or blocked filter under the venturi cap.Related: gas valve and supply
- F.54Get it checkedA gas supply fault, usually shown alongside F.28 or F.29. It means gas is reaching the appliance at too low a pressure.Related: gas valve and supply
- F.26Get it checkedVaillant call this "fuel valve not working": the stepper motor that drives the gas valve is not responding, so the boiler cannot open the gas and will not light.Related: gas valve and supply
- F.42Get it checkedA fault with the coding resistor, the small component that tells the board which gas the boiler is set up for. The boiler will not run until it knows.Related: gas valve and supply
Own a Vaillant 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
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.