Viessmann Boiler F0 Fault Code
The Viessmann fault code F0 relates either the air lock, blockage or pump failure and here we have Q & A or require an engineer for an emergency boiler repair.
The Viessmann Boiler Fault Code F0 Error Common Q & A
Just below, we have a list of common questions relating to the F0 fault code on the Viessmann Boiler.
- What does the F0 fault code mean on my Viessmann boiler?
- If I reset my boiler, will this fix the F0 fault code?
- How could air locks have contributed to the F0 fault code being displayed on my Viessmann boiler?
- Where do air locks occur, and how can they be removed from my heating system?
- What kind of air locks can be removed on a DIY basis?
- Should I reset my boiler after bleeding all radiators and towel rails?
- What kind of blockages should my boiler repair company expect to find?
- How can limescale and heating sludge be removed?
- After a hot flush, what can be done to stop these blockages occurring again?
- If the pump is causing the F0 fault code to be displayed, where should my boiler engineer start?
- If my pump has no power, what is the likely cause of the fault?
- How much is a replacement pump going to cost on my Viessmann boiler?
What does the F0 fault code mean on my Viessmann boiler
If you’re having problems with your Viessmann boiler, it will show a fault code on the display panel.
The F0 fault code relates to one of the following:
- Air lock in the heating system
- Blockage in the boiler, pipes or radiators
- Pump failure
Once a fault code has been shown on the display panel, it’s likely your boiler is going to lockout. This lockout is going to mean that your boiler doesn’t work until your boiler engineer fixes the problem and resets the appliance.
If I reset my boiler, will this fix the F0 fault code
Resetting your boiler isn’t going to fix the F0 fault code. The boiler should only be reset after a Gas Safe engineer has fixed the problem. And, that’s because the lockout function is designed to ensure that the boiler is safe, and no more expensive parts are exposed to further damage.
How could air locks have contributed to the F0 fault code being displayed on my Viessmann boiler
Air locks can reduce the pump’s ability to circulate water around the heating system. It’s likely that a small system leak has allowed air into the system. Eventually, the air locks will become so big, that the boiler can no longer work efficiently, and so the boiler locks out.
Your boiler repair company will need to find the origin of the leak, to ensure air locks don’t enter your system again, but also remove the current air locks.
Where do air locks occur, and how can they be removed from my heating system
Some air locks can be removed on a DIY basis. One air lock that may need to be removed that can’t be done on a DIY basis, are air locks in central heating pumps.
To access the pump, the boiler needs to be taken apart, and that should only be done by qualified Gas Safe engineers.
Once they have access to the pump they’ll be able to use the bleed screw to allow air to escape from the system.
What kind of air locks can be removed on a DIY basis
A quick fix that you can try on a DIY basis to remove air locks, is to bleed towel rails and radiators in your central heating system.
You’ll need a radiator bleed key, these can be purchased from most DIY and hardware stores.
Making sure you protect walls and flooring, carefully open the valve on your radiator. You’ll notice that the radiator starts hissing; that’s a sign that air in the system is being released. Once all air has been released, the hissing noise will be replaced by a steady flow of water. At this stage, you can close the valve on that radiator, and move onto the next one.
Should I reset my boiler after bleeding all radiators and towel rails
There’s one more step you’ll need to complete before resetting your appliance; checking the boiler’s pressure. After letting air escape from the system, it’s likely that the pressure on your boiler has dropped dramatically.
For modern boilers to work efficiently, they need to be set around 1.3 bar; check your owner’s handbook for the pressure your boiler needs to be set at.
If you notice the pressure gauge on the front of your boiler has dropped below 1.3 bar, it will need to be topped up. And, you’ll be able to do this by adding water to the central heating system via the filling loop.
The filling loop is usually located just beneath the boiler’s casing and pressure gauge; it’s a small braided hose. Opening the valve will allow water to enter the system and in turn, will increase the boiler’s pressure.
After filling the boiler up, if you notice the pressure is too high, you’ll be able to reduce pressure by removing water from the system. This can be done via the drain cock. If you can’t find the drain cock, you’ll need to remove water by opening the bleed valve on a radiator instead.
What kind of blockages should my boiler repair company expect to find
If a blockage has caused the F0 fault code to be displayed on your Viessmann boiler, it’s likely they’ll be in the form of heating sludge or limescale.
Limescale is the most likely cause of a blockage if you live in a hard water. For all other areas, heating sludge is the most common cause of a blockage.
Regardless of the type of blockage, each will lead to the pump not being able to circulate water around the heating system correctly. As soon as your boiler’s PCB notices this, it’s going to lockout and display the F0 fault code, to avoid parts being overworked, and sidestepping expensive repair bills.
How can limescale and heating sludge be removed
Both blockages can usually be removed by running a hot flush. This basically means working the boiler at a high temperature, after dosing the system with specifically designed cleaning chemicals. Once the system is drained, heating sludge could have been removed.
The way to move the harshest of blockages, is a central heating power flush. This is a hot flush, but at a high pressure. Although this can remove more blockages than a basic flush, it’s not without risks. A central heating power flush can put old heating systems under excess strain, sometimes causing leaks. And with newer systems that are more likely to withstand the pressure, it’s unlikely the blockages are harsh enough to warrant the power flush in the first place.
After a hot flush, what can be done to stop these blockages occurring again
If you want to protect your system from future blockages, your boiler engineer will be able to install some preventive measures.
The first thing they’ll do, is ensure that your system is topped up with central heating inhibitor; this helps to break down limescale and central heating sludge.
But, this limescale and heating sludge needs to then be removed from the system. For hard water areas that are affected by limescale, a limescale filter will do the job. And alongside a limescale filter (and for areas without hard water), a magnetic system filter will be installed to catch heating sludge.
Remember, these filters need to be cleaned out. Once they’re full, they’ll no longer be protecting your boiler from a blockage. We advise getting both filters cleaned out with your annual boiler service.
If the pump is causing the F0 fault code to be displayed, where should my boiler engineer start
The hot flush and bleeding of the pump via the air screw, mentioned above, will have ensured that the pump isn’t blocked, ensuring its ability to circulate water around the heating system.
So, now they’ll need to focus their attention on the general condition of the pump, and its communication with the PCB. To start, that’s going to mean testing wiring and connections with a multi-meter, looking for weak or non-existent power. Any issues with wiring will lead to intermittent pump operation, and these issues need to be fixed as soon as possible.
Next, they’ll want to check that the pump isn’t stuck. This is a mechanical device that can wear over time, and eventually, that’s going to mean that it starts sticking. If the pump is extremely hot, it’s likely it’s either blocked, or in this case, it’s stuck. A gentle tap can usually free the pump. But, your boiler repair company will want to assess the pump’s overall condition, as a replacement might be a better option than a repair.
Finally, they’ll want to ensure that the pump’s speed settings are correct. Newer pumps have up to three speed settings. It might be that the pump is on too low of a speed setting, not being able to produce the flow rate of required for your large central heating system. This can be adjusted to suit your property.
If my pump has no power, what is the likely cause of the fault
Not all pumps can be fixed. Whether that’s the pump having no power, or simply not responding to demand from the PCB, it might be that a replacement is going to be needed.
How much is a replacement pump going to cost on my Viessmann boiler
If a replacement pump is what’s needed to fix the F0 fault code on your Viessmann boiler, you should expect to budget around £250, including parts and labour.
For boilers that are well within warranty, and whereby other expensive parts (the PCB, heat exchanger, gas valve and fan) are in good condition, the most cost effective option would be to replace the pump to repair the appliance, rather than replacing the boiler completely.
Other Viessmann boiler issues
For more boiler issues regarding the Viessmann Boiler then please visit the Ideal Boiler Problems And Cures page.