Vaillant F.41 fault codewhat it means and how to fix it
A turboMAX plus 837 or thermoCOMPACT 637 code only: the board has no gas type stored, usually after a PCB change, and an engineer must set natural gas or LPG in the P programmes.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.41
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.41 means
F.41 is printed in one Vaillant table, for the turboMAX plus and thermoCOMPACT ../2 E, marked "837/637 only": "no setting for the type of gas is stored — set gas type in PCB (see page 30)". The 37 kW models controlled their fan speed and burner pressure electronically, so the board had to know which gas it was burning, and that setting lived in memory rather than on a jumper.
If the memory is blank — a new board fitted and not commissioned, or a board whose stored settings have been lost — the boiler refuses to run rather than fire on the wrong curve. Page 30 of the manual is the mid-setting point procedure: with the boiler switched off, the "+" button is held while the main switch is turned on until the display cycles through the P numbers, and "P11" (natural gas) or "P13" (LPG) is selected before the burner pressure is checked against 5.3 mbar for natural gas or 15.3 mbar for LPG. That is a commissioning task with a manometer on the gas valve and is the engineer's alone; it is not a householder setting and the operating instructions do not mention it.
F.41 has no relative in any later Vaillant table. The ecoTEC ranges store the gas group differently and report a mismatch as F.92, which is a different fault with a different remedy. An owner seeing F.41 has an 837 E or 637 E from 1999 to 2005 that has, almost always, just had its board replaced.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| New control board not yet set up | The usual case. A replacement PCB leaves the factory without a gas type stored, and F.41 appears the first time the boiler is switched on until P11 or P13 is selected. | Common |
| Stored settings lost | A board whose memory has failed forgets the gas type along with everything else. Often accompanied or followed by F.63. | 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
Setting the gas type is a commissioning step, £80 to £120 as a stand-alone visit and nothing if it is completed as part of the board replacement it follows.
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
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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.