Viessmann F9 Fault

February 15, 2023

The F9 fault is a fan fault, which means the fan is running when it shouldn't. The fan's job is to pull warm air out of the boiler. If an F9 occurs, the boiler controller will turn off the pump and call for a service technician to inspect it. It's not uncommon for an F9 to be caused by a clog in the heat exchanger or a foreign object in the fan.

This fault can occur any time the unit is in use and will restart whenever there is a power interruption. It can also happen when there are higher than normal room temperatures or high humidity levels.

This fault must be rectified as soon as possible because if left alone for an extended period, this faulty relay will cause damage to your compressor and other components.


What Does The F9 Fault Code Mean On My Viessmann Boiler?

If your boiler is displaying an F9 fault code, it means that there is a problem with the fan. The fan is used to keep the combustion chamber hot enough to burn fuel and produce heat. If the fan stops or doesn't work properly, this will cause problems with your boiler's efficiency.

To troubleshoot this issue, you need to check the following:


The air filter

If this isn't clean and free from blockages, it could affect air flow into your boiler. Check whether it's clean and if not, clean it out thoroughly. You may need to use compressed air to blow out any dust or dirt accumulated inside of it.

The heat exchanger

This part of the system helps transfer heat from one side of the boiler to another; if there is any damage or cracks in this section, then this could be causing issues with how well the fuel is being burnt in your boiler. Check for any cracks or chips on this part of the system, as these can allow air through, which will affect efficiency levels.


If I reset my boiler, will it fix the fan and the F9 fault code on my Viessmann boiler?

Resetting the boiler will fix the fan and F9 fault code; If there is no gas supply to your boiler, it will not be able to heat up. The boiler will try to run, but it will not be able to generate any heat. If you reset the boiler, the system will start again and run through its diagnostics. This can sometimes fix minor issues such as an F9 fault code.

It is also possible that there is a problem with your control board, which sends signals to the fan and other parts of your boiler. This could cause an F9 fault code to appear on your display screen. In this case, it is best to call a professional engineer who can diagnose the issue and repair it for you.

What Does The Fan Do On My Boiler?

The fan is one of the essential parts of your boiler, as it is responsible for circulating air through the room and heating it. The fan can be run manually or automatically, depending on how you set up your system.

When the boiler is turned on, the fan will also turn on automatically. The fan will continue to run until all of the hot water has been used, at which point it will turn off automatically. If you have a manual mode on your boiler, you will need to turn this off yourself when you are not in your home.

The main function of the fan is to circulate air around so that it heats up more quickly and evenly in different rooms within your home. This prevents cold spots from forming in certain areas and allows heat to spread throughout each room more efficiently. It also helps to prevent mold growth where water may be trapped in corners or underneath furniture because no air circulation prevents moisture from building up in these areas.

Why Would The Fan Still Be Running After The Burner Has Shut Down

Fan running after the burner shuts down.

This is a common problem and happens to almost every Viessmann boiler with a gas condensing boiler. The fan will continue to run for a short time after the burner shuts off until the radiator has cooled down enough so that it can no longer produce condensation.

A typical scenario would be that you have set your thermostat at 20 deg C, but when you come home from work, the house is still warm. This may be because there is still some heat left in the radiators, and they are still producing condensation. The fan is then enabled to cool them down, so they stop producing condensation. This process takes between 30 minutes and an hour, depending on how much heat was in the radiators and how big they were (the bigger they are, the longer it takes).


If There Are Wiring Issues With My Fan, Can These Be Fixed

If there are wiring issues with your fan, these may be repaired by a qualified technician. However, if the wiring is damaged to the extent that it cannot be repaired, it may be necessary to replace the entire unit.

Suppose your fan will not turn on and you have checked all the things mentioned above. In that case, you may want to check with a professional electrician or appliance repairman to determine if there is an electrical issue with your unit. If so, they will be able to decide on what needs to be done for it to work properly again.


How Can My Boiler Engineer Test The Fan

The boiler engineer should be able to test the fan by looking at the display.

If the boiler is running and there is no display, it could be a faulty PCB or main board. This can be tested by checking that the small circuit board inside the boiler is not damaged and has power going to it. The other thing to check is if there are any loose connections between this and other parts in the boiler system.

If there is no display with no power going to the small circuit board, it could be a faulty fan motor (which will need replacing).


My Fan Needs Replacing; How Much Is This Going To Cost

If your boiler's fan is faulty, it will need to be replaced. This can be done by a qualified engineer, but if you wish, they can take care of the entire process for you.

The engineers have extensive experience with this issue and will make sure that everything is done correctly.

The cost of replacing a faulty fan motor depends on several factors:

  • The model of your boiler.
  • Where you live (local labor rates)
  • How long does it take to complete?

In general, you can expect to pay around £250 to replace your fan.



In the end, if the problem lies with your thermostat, the simplest way to solve it is to replace it. Obviously, this isn't always physically possible, nor is it economical for many homeowners. But if you want a long-term solution to your problem, you'll want to take this route. It might be wise to call a professional as well, since they'll likely have the tools and expertise needed.

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