Viessmann F4 Fault Code Explained
Hertfordshire, Bedfordshire & Cambridgeshire
If your Viessmann boiler is showing F4, here is something no other page will tell you: Viessmann’s own published UK fault-code list does not include F4 at all. Almost every article you will find states a confident definition for it, and not one of them cites a Viessmann source.
We are a Gas Safe registered heating firm, not a content site, so we would rather tell you what is actually documented than repeat something we cannot stand behind. Here is where that leaves you, and what to do next.
What Viessmann actually publishes
Viessmann UK’s official fault-code checker lists the following codes. Every one of them relates to the fan or its plug-in connections:
- F6, fan or fan connection
- F9, fan or fan connection
- F-E1, fan or fan connection
- F-E2, fan or fan connection
- F-F6, fan or fan connection
F4 is not on that list. That does not mean your display is wrong, and it does not mean your boiler is fine. It means the code needs reading against your specific appliance and generation rather than against a general list found online.
Check the code carefully before you act on anything
Viessmann displays can be hard to read, and an F4 is easily confused with an F-E1, an F-E2 or a partially lit F6. All three of those are published, and all three point at the fan or its connection.
If you can, photograph the display. It costs nothing and it is the single most useful thing you can hand an engineer.
Why the advice you will find for Viessmann F4 does not agree
Search F4 and you will be told, flatly, that it means one specific thing. Different pages give different answers, and none of them cite Viessmann.
We checked. Viessmann UK’s fault-code checker does not list F4. The Vitodens 100-W operating and service documentation we could obtain gives a fault-diagnosis table organised by symptom rather than a list of F codes. So the confident definitions circulating online are not coming from Viessmann.
We are not going to add another one. On a gas appliance, a plausible guess is worse than an honest gap, because it sends you or your engineer looking at the wrong component.
What to do if your boiler is displaying F4
These are safe checks that apply to any locked-out boiler. None of them assumes a diagnosis:
- Photograph the display. Note the exact characters and whether anything is flashing.
- Check your other gas appliances. If the hob will not light either, the problem is the gas supply, not the boiler. Check prepayment meter credit if you have one.
- Check the pressure gauge. It should sit between 1 and 1.5 bar with the heating off.
- Check the condensate pipe if it is cold outside. A frozen condensate pipe locks boilers out across every manufacturer.
- Find your model and serial number. They are usually on a label behind or beneath the front panel. An engineer can look the code up properly against your exact appliance.
Then stop. Do not sit and reset it repeatedly. A boiler that locks out is protecting itself, and repeated resets on an appliance that will not hold a flame send gas to an unlit burner.
If you smell gas, stop reading and act
Getting it read properly
A Viessmann-trained or Gas Safe registered engineer can interrogate the appliance directly rather than relying on a published list. That is the correct route for a code that the manufacturer does not publish publicly.
Vantage Plumbing & Heating is Gas Safe registered and works across Hertfordshire and Bedfordshire. If your boiler has locked out and you are in our area, call us and we will read the code against your actual appliance.
Frequently asked questions
Does F4 on a Viessmann boiler mean no flame detected?
We cannot tell you that it does. Viessmann UK’s published fault-code list does not include F4, and the definitions circulating online do not cite a Viessmann source. On a gas appliance we are not prepared to repeat a definition we cannot verify. Have the code read against your specific model.
What fault codes does Viessmann actually publish?
Viessmann UK’s fault-code checker lists F6, F9, F-E1, F-E2 and F-F6. All of them relate to the fan or its plug-in connections.
Could I be misreading the display?
It is worth ruling out. F-E1, F-E2 and F6 are all published codes and all can be misread as F4 on a small or partially lit display. Photograph it if you can.
Can I keep resetting my boiler?
No. A boiler locks out to protect itself. Repeatedly resetting an appliance that will not hold a flame sends gas to an unlit burner, and some manufacturers log excessive resets as a fault in their own right.
Is a Viessmann F4 dangerous?
When to call an engineer
Still stuck? We repair this fault regularly across Hertfordshire, Bedfordshire and Cambridgeshire. Call 01462 506374 to get an engineer booked, or to talk it through first if you would rather. Genuine 24 hour cover, 365 days a year.
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