Viessmann FF Fault Code: Vitodens 100-W Causes, Reset Advice and Spares
Estimated reading time: 6 minutes
If your Viessmann Vitodens 100-W boiler is showing an FF fault code, the boiler has entered a safety lockout and needs attention.
On Vitodens 100-W models that use this fault-code format, FF usually means the burner has been blocked because the boiler has detected a fault in the burner control circuit. This can involve the ignition electrodes, their connecting cables, electrical interference or the burner control unit itself.
The FF code is not the same as the Viessmann F4 fault code. F4 relates to no flame signal being detected, while FF is more closely linked to the boiler’s burner control system.
Quick Answer
The Viessmann FF fault code on a compatible Vitodens 100-W boiler usually points to a burner control unit fault.
You can try one reset using the correct procedure for your boiler. However, if the FF code returns, the boiler should be checked by a Gas Safe registered engineer. The engineer may need to inspect the ignition electrodes, connecting leads and control board before deciding whether a replacement part is needed.
Table of contents
What Does the Viessmann FF Fault Code Mean?
The burner control unit manages important parts of the boiler’s ignition and safety sequence.
When the boiler displays FF, it means the burner has been blocked because the boiler has identified a potential fault in this control system. It does not automatically mean that the PCB has failed, but the control board may need further investigation if the fault keeps returning.
Because Viessmann fault codes can vary between boiler generations, always check the exact model shown on the boiler data plate before ordering parts or following reset instructions.
Viessmann FF vs F4 Fault Code
It is important not to confuse FF with F4.
| Fault Code | Means | Main Area to Check |
| FF | Burner control unit fault | Ignition electrodes, connecting cables, electrical interference and control unit |
| F4 | No flame signal detected | Ignition system, flame sensing, gas supply, gas valve and related components |
Both faults can stop your heating and hot water, but they should not be diagnosed in exactly the same way.
What Can Cause an FF Fault Code?
Several issues may lead to an FF code on a Vitodens 100-W boiler.
Ignition Electrode Problems
The ignition electrodes help the boiler light safely and confirm correct burner operation. If an electrode is worn, damaged, contaminated or not positioned correctly, the boiler may enter a fault condition.
Damaged Ignition Leads or Connections
The cables connecting the electrodes to the boiler control unit can become damaged, loose or worn over time. A poor connection may affect the burner control circuit and trigger an FF code.
Electrical Interference
In some cases, strong electrical interference near the boiler can affect the control system. This is not something a homeowner can diagnose safely, but it is part of the engineer’s fault-finding process.
Burner Control Unit or PCB Fault
If the ignition electrodes, leads and electrical connections are in good condition, the burner control unit may be at fault. Depending on the boiler version, this may be referred to as the control board or PCB.
A replacement PCB should not be ordered based on the fault code alone. The boiler needs proper diagnosis first.
Safe Checks for Homeowners
There are a few safe checks you can make before arranging an engineer visit.
First, take a clear photo of the FF code on the boiler display. Also take a photo of the boiler data plate if possible, as this helps identify the exact Vitodens 100-W version.
Check whether the boiler has power and whether there has recently been a power cut or electrical work in the property.
You can also check whether other gas appliances, such as a gas hob, are working. This may help identify a wider gas-supply issue, although it does not confirm the cause of the FF fault.
Do not remove the boiler case, touch any internal wiring, clean electrodes or attempt to replace the PCB yourself.
How to Reset a Viessmann Vitodens 100-W FF Fault
Try one reset only.
On some Vitodens 100-W boilers with an R reset button, press or touch the reset button for around two seconds. On older versions, the reset method may involve a rotary selector instead.
Use the instructions for your exact boiler model. Do not keep resetting the boiler if the FF code returns.
If the boiler restarts and continues working normally, keep an eye on it. If FF appears again, book a Gas Safe engineer to diagnose the issue.
When to Call a Gas Safe Engineer
Call a Gas Safe registered engineer if:
The FF code returns after one reset.
The boiler has no heating or hot water.
The boiler makes unusual noises before locking out.
You can see damaged cables or signs of water damage around the boiler.
You smell gas or suspect a gas leak.
If you smell gas, do not operate electrical switches or attempt to reset the boiler. Leave the property and follow the correct gas-emergency procedure.
What Will an Engineer Check?
An engineer may inspect the ignition electrodes and connecting leads first.
They may then check the boiler’s electrical connections, look for possible interference affecting the control system and assess whether the burner control unit is operating correctly.
If the FF code remains after these checks, the engineer may recommend replacing the burner control unit or PCB. The correct part depends on the boiler model, serial number and existing part number.
Viessmann Spares That May Be Related
Depending on diagnosis, parts linked to an FF fault may include:
Ignition electrode assembly
Ignition or electrode lead
Burner control unit
Boiler PCB or control board
Always check the boiler model, serial number and existing part number before ordering a Viessmann spare.
Need Viessmann Spares?
Heating & Catering Parts supplies a range of Viessmann spares for compatible Vitodens boilers.
Before ordering a PCB, ignition electrode or burner control unit, make sure the fault has been diagnosed correctly. Send us a clear photo of the boiler data plate and the existing faulty component to help identify the right replacement part.
Related Guides
[Viessmann F4 Fault Code]
[Viessmann F2 Fault Code]
FAQs
Not necessarily. On relevant Vitodens 100-W models, FF is linked to a burner control unit fault. F4 is the separate code commonly associated with no flame signal.
You can try one reset using the correct procedure for your boiler model. If the code returns, contact a Gas Safe engineer.
Not always. The ignition electrodes, leads and electrical connections should be checked before the control board is replaced.
Low system pressure is not usually the main diagnostic route for an FF fault. However, your engineer should still check the overall boiler condition during diagnosis.
No. PCBs, internal wiring and burner-control components should only be handled by a qualified engineer.
Key Takeaways
- The Viessmann FF fault code indicates a burner control unit issue, requiring attention if it persists after a reset.
- You should not confuse the FF code with the F4 fault code, which refers to a no flame signal.
- Common causes of the FF fault include problems with ignition electrodes, damaged connections, or electrical interference.
- Homeowners can perform safe checks, but any repairs should be left to a Gas Safe registered engineer.
- Parts related to the FF fault may include the ignition electrode assembly, burner control unit, or boiler PCB.
