Vaillant F.92 Fault Code: Causes, Fixes & Repair Costs
What does the Vaillant F.92 fault code mean?
The F.92 code on a Vaillant boiler signals a gas group configuration mismatch. In practical terms, the coding resistor fitted to the PCB does not correspond to the gas family that has been entered into the boiler's settings — or the gas family check was not completed correctly during commissioning. Because the boiler cannot confirm it is configured for the correct gas type, it locks out as a safety precaution. This fault is almost always rooted in a commissioning or configuration error rather than a mechanical failure, making it a job for a Gas Safe registered engineer rather than a component replacement.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Coding resistor mismatch on the PCB Common
Each Vaillant boiler uses a coding resistor on the PCB to identify the correct gas family. If this resistor is incorrect, missing, or has a poor connection, the boiler's software detects a conflict with the entered gas group setting and triggers F.92. This is the most frequent root cause, particularly after a PCB swap or service visit.
- Incorrect gas family entered in the boiler's configuration menu Common
During commissioning or after a service, the gas family parameter in the boiler's configuration menu may have been set incorrectly — for example, entering a setting for LPG when the boiler is connected to natural gas (or vice versa). Even if the resistor is correct, this settings mismatch alone is enough to cause F.92.
- Gas family check terminated before completion Sometimes
Vaillant boilers run an automated gas family verification routine during commissioning. If this process is interrupted or not fully completed — perhaps due to a power cut or an engineer exiting the menu prematurely — the boiler records an incomplete check and displays F.92 at the next startup.
- Combustion quality outside permitted limits Sometimes
Poor combustion readings — caused by a wrong gas restrictor, a blocked internal pressure measuring point in the venturi, or recirculation of flue gases — can push the boiler outside its acceptable operating envelope and contribute to a gas group fault. Note: lubricant must never be applied to the O-ring in the venturi, as this can block the pressure measurement point.
- Faulty or damaged PCB Rare
In rare cases the PCB itself is damaged, causing it to misread the coding resistor signal even when the resistor is physically correct. A failed PCB is an expensive outcome but is the least likely explanation for F.92 in isolation.
How to fix it
- Attempt a boiler reset DIY safe
Press and hold the reset button on the boiler's control panel for the time stated in your user guide (typically 3–5 seconds). Wait for the boiler to restart and observe whether F.92 returns. For a configuration fault like F.92, a reset rarely resolves the underlying issue, but it is worth trying once or twice before calling an engineer. Do not reset more than 2–3 times.
- Check that the gas supply to the property is live DIY safe
Confirm that other gas appliances — a hob or gas fire, for example — are working normally. If your gas supply has been interrupted, contact your gas supplier before doing anything else. If the supply is fine, the fault is almost certainly a configuration issue within the boiler.
- Do not attempt to access the boiler's internal components or engineering menus Gas Safe engineer
The configuration parameters that cause F.92 sit in the boiler's installer or service menu and relate directly to gas-type settings. Changing these incorrectly could cause the boiler to operate on the wrong gas group — a serious safety hazard. Only a Gas Safe registered engineer should access these menus.
- Have a Gas Safe engineer verify and correct the gas family setting Gas Safe engineer
An engineer will access the boiler's service menu, check the gas family parameter, and compare it against the coding resistor value on the PCB. If the setting is wrong, they will re-enter the correct gas group and re-run the gas family verification routine to clear the fault.
- Have the engineer check the coding resistor and its connections Gas Safe engineer
The engineer will inspect the coding resistor for continuity and confirm it matches the boiler model and gas type. A corroded connector or an incorrect resistor from a previous PCB replacement are common findings. If the resistor is faulty or wrong, it will be replaced.
- Have the engineer inspect the venturi and gas restrictor Gas Safe engineer
If the gas family check keeps failing, the engineer should check the venturi's internal pressure measurement point for blockages and confirm the correct gas restrictor is fitted. No lubricant should be applied to the venturi O-ring during this check.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
Because F.92 is fundamentally a gas configuration fault, all meaningful diagnostic and repair work must be carried out by a Gas Safe registered engineer. Contact Vaillant's service line on 0330 100 3143 or arrange a visit through an independent Gas Safe registered heating engineer. Attempting to fix this fault yourself is unsafe and may invalidate your boiler warranty.
Parts you may need
- Coding resistor (gas group resistor) · from £15
- PCB (printed circuit board) · from £220
- Venturi assembly · from £65
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £90–£220, depending on the underlying cause.
Frequently asked questions
Can I fix Vaillant F.92 myself by resetting the boiler?
A reset is worth trying once or twice — it costs nothing and occasionally clears a transient fault. However, F.92 is caused by a mismatch between the boiler's gas family configuration and the coding resistor on the PCB. A reset does not change any settings, so in the vast majority of cases the fault will return immediately. You will need a Gas Safe registered engineer to access the service menu, correct the gas group setting, and re-run the verification routine.
Why has F.92 appeared after a recent service or PCB replacement?
This is the most common scenario for F.92. When a PCB is replaced, the new board may come fitted with a coding resistor for a different gas group, or the engineer may need to re-enter the gas family setting from scratch. If the commissioning step is skipped or completed incorrectly, F.92 will appear at the next startup. Contact the engineer who carried out the work — resolving a commissioning oversight on their part should be covered under their call-back policy.
How much does it cost to fix Vaillant F.92 in the UK?
If the fix is purely a configuration correction — re-entering the gas family setting and re-running the check — you are typically looking at a call-out and one hour of labour, coming to roughly £90–£150 depending on your region and the engineer's rates. If the coding resistor itself needs replacing, add a small parts cost (around £15), keeping the total in a similar range. In the unlikely event that the PCB is faulty and needs replacement, costs rise to £300–£500 including parts and labour; however, this is rarely the cause of F.92 on its own.
Is my Vaillant boiler safe to use with an F.92 fault showing?
No — when F.92 is active, the boiler locks out and will not fire. This is a deliberate safety measure: the boiler refuses to operate when it cannot confirm the correct gas configuration is in place. Do not attempt to bypass the lockout. Leave the boiler off and arrange for a Gas Safe registered engineer to visit as soon as practical, especially during cold weather.