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Viessmann Boiler F FB Fault Code

The Viessmann fault code F FB relates to the fan not stopping and here we have Q & A or require an engineer for an emergency boiler repair.


The Viessmann Boiler Fault Code F FB Error Common Q & A

Just below, we have a list of common questions relating to the F FB fault code on the Viessmann Boiler.

Viessmann boiler error code F FB
  • What does the F-FB fault code mean on my Viessmann boiler?
  • Can I fix the F-FB fault on a DIY basis?
  • When should the fan be running on my boiler?
  • Is it dangerous to have a fan that’s constantly running?
  • What are the most likely causes of the F-FB fault code being displayed?
  • How could the fan be to blame for the F-FB fault code being displayed?
  • How will my boiler engineer know if wiring and connections are the problem?
  • If the fan is the problem, how will my boiler repair company know?
  • I need a new fan in my Viessmann boiler, how much is this likely to cost?
  • If the PCB is the issue, how will my boiler engineer know?
  • If I need a new PCB, how much is this going to cost to replace?

What does the F-FB fault code mean on my Viessmann boiler

Your boiler is controlled by the printed circuit board (PCB). This is the component that communicates with all important electronic parts, to ensure that the boiler is operating smoothly.

If you’re seeing the F-FB fault code being displayed on the control panel of your boiler, it means the fan hasn’t stopped, and the burner has gone into fault mode.

The boiler has given the signal for the fan to stop, but it continues to run without demand.

Can I fix the F-FB fault on a DIY basis

To fix the F-FB fault code on Viessmann boilers, the boiler will need to be taken apart. And, taking a boiler apart is a job that should only be completed by Gas Safe engineers. So, there isn’t a DIY fix.

Also, you shouldn’t reset your boiler. The reset function should only be used after the problem that has caused the fault code to be displayed, has been rectified.

It’s likely your boiler has locked out, so it no longer works. Typically, this lockout is put into place either to protect internal boiler components from further damage, or to make sure the boiler isn’t dangerous.

As the PCB can’t be sure why the fan is still running or whether the boiler is dangerous, it locks out as a safety precaution.

Call a Gas Safe registered boiler repair company. They’ll be able to fault-find, fix the problem, and they’ll then reset your boiler to clear the fault code on your Viessmann boiler.

When should the fan be running on my boiler

The fan on your boiler is incredibly important. It’s the component that ensures that harmful gases aren’t contained in the boiler, and instead, are vented out of the property.

On the exterior of your property, you’ll notice a flue (usually a large white pipe going through a wall or roof). When the boiler fires up, you’ll notice this steaming. These are flue gases being vented from the property.

The job of the fan is to ensure that a big enough draft is created inside the boiler, so these gases can escape. Before your boiler ignites, the PCB wants to see a signal from the fan, that it’s fired into life. If it hasn’t, the boiler won’t work and will lock out.

The only time your fan shouldn’t be running in your boiler, is when the there is no demand for heat, and the burner shuts down. But, in the case of the F-FB fault code, it seems the fan is running, even when the boiler isn’t producing a flame.

Is it dangerous to have a fan that’s constantly running

It’s unlikely that your boiler is dangerous. For a start, the F-FB fault code is likely to lead to a lockout, and that means your boiler won’t be firing.

But, the lockout function is important in other ways too. For instance, if your fan is constantly running, that means it’s getting extra wear and tear which will lead to its life being shortened. Fans are not particularly cheap to replace, so the lockout is going to prevent you from being exposed to extra repair bills.

What are the most likely causes of the F-FB fault code being displayed

Although the F-FB fault code relates directly to the fan, that’s not the only potential cause of the error. Your boiler engineer will need to check the fan and PCB.

How could the fan be to blame for the F-FB fault code being displayed

The fan is a complicated electrical component, and it relies on a range of signals, to work correctly, but at the right times too.

Your boiler engineer will want to check the following:

  • 100A cable
  • All wires and connections
  • Fan unit

If wiring is the issue, the first place to start is the 100A cable to the fan. This is the most likely cause of the fault. Your boiler engineer can test this using a multi-meter to determine whether it’s faulty and replace it if necessary.

How will my boiler engineer know if wiring and connections are the problem

If the main 100A cable to the fan isn’t the problem, your boiler engineer will focus their search on the wires and connections to and from the fan. These could have become damaged due to wear and tear, boiler vibrations, or even water damage.

Any small sections of wiring that are damaged can be replaced. And, if there’s an intermittent signal between the PCB and the fan, it’s likely there are connections that aren’t secure. These will need to be secured to install communication between the two components.

If the fan is the problem, how will my boiler repair company know

The fan will need to be tested, just as any other electrical component would, using a multi-meter. The multi-meter will determine whether the fan is getting power. Your boiler repair company will have already tested all wiring and connections. So, if the fan isn’t getting power, it’s this component that needs to be changed.

I need a new fan in my Viessmann boiler, how much is this likely to cost

Whilst boiler fans aren’t the most expensive components in a boiler to replace, they’re certainly not cheap. Depending on the model of Viessmann boiler you have, you should expect to pay in the region of £225-300.

That’s going to be the price including parts and labour; expect the job to take one working day to complete.

If the PCB is the issue, how will my boiler engineer know

Communication goes two ways. Just as the communication or power issue could be due to the fan, it could be due to the PCB too.

But, if the PCB is the problem, it’s likely that your boiler has been working intermittently and sporadically for a while. And, that’s because it controls all the most vital electronic components in your boiler.

Sporadic operation includes the likes of the appliance cycling on and off, components operating (or not) when the shouldn’t (such as the fan), and the LED display going on and off at times.

To determine whether the PCB is at fault, your engineer will test it, just as they did with the fan. Using a multi-meter, they’ll test wires, connections and the PCB itself to determine where the problem lies.

If I need a new PCB, how much is this going to cost to replace

Boiler repair companies will replace PCBs as a last resort. And, that’s because they’re one of the most expensive components in a boiler to replace. You should expect to pay anything between £400-500 for a new one.

And, we’d always suggest getting a general health check for your boiler when spending this amount of cash. Your engineer can check expensive components such as the gas valve, fan, PCB, heat exchanger and pump.

If other expensive and important components are about to fail, on top of the £400-500 repair bill you’re already facing, it might be worth considering getting a quote for a new boiler.

Other Viessmann boiler issues

For more boiler issues regarding the Viessmann Boiler then please visit the Ideal Boiler Problems And Cures page.