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Viessman Boiler Problems, Service & Repairs

Got a Viessman fault! looking for a cure before it comes too much of a problem or require an engineer for an emergency boiler repair.

Viessman Boiler Problems, Service & Repairs

Below we’ve written up a detailed guide to Viessmann boiler faults, and what needs to be done to fix them including a link to individual articles.

When a boiler develops a problem, a fault code is displayed on the control panel. This gives an indication of what the problem is, allowing your boiler engineer to fix the problem quicker than if they had to fault-find every single part in your boiler. And, that’s going to save lots of time, as well as money when it comes to repair bills.

On some occasions, your boiler will lockout. This means your appliance won’t work until the problem has been found and fixed. Once your boiler repair company has completed the fix, they’ll reset your appliance on your behalf.

Although below there are some problems that can be fixed on a DIY basis, most problems will require a Gas Safe registered engineer to diagnose and fix the problem.

The Viessmann fault codes covered below include:

Vaillant Boiler F22 Fault Code Error

If my Viessmann boiler is showing fault code 10 on the display panel, what does this mean?

The 10 fault code on Viessmann boilers relates to no flame signal being present. Your Gas Safe boiler repair company will first need to check that the flame sensor is functional. If it’s not, the printed circuit board (PCB) won’t recognise a flame as being present, even if it is.

If the issue doesn’t relate to the flame sensor, your engineer will need to fault-find by checking anything that could hinder the boiler’s ability to establish a flame. This includes:

  • Checking the gas pressure into and out of the meter, as well as the boiler
  • Ensuring the flue and condensate aren’t blocked
  • Checking for debris build-up in the burner and jet
  • Ensuring the PCB doesn’t have an electrical fault.

If fault code 14 is being shown on the display panel of my Viessmann boiler, is there a quick fix?

The 14 fault code is like the 10 fault code and occurs on the Vitodens 200. If this fault code is being displayed on your boiler, your engineer will need to check for electrical issues, then move onto anything that is going to hinder your boiler’s ability to create a flame.

The PCB is the component that controls all electrical parts in your boiler. So, it’s likely your boiler repair company will test this first, using a multi-meter. They’ll also go ahead and test the flame sensor to ensure it’s getting power. If either of these parts are lacking in power, they’ll need to be replaced.

But, if both components are in good condition, it’s likely a gas supply issue. This could mean anything from a blocked jet in the burner, lack of gas pressure, or even a gas valve that’s sticking partially closed.

Fault code 0B is being displayed on my Viessmann boiler, what is the problem?

The OB fault code is usually limited to one of two scenarios:

  • The burner and/or jet are blocked
  • The pump is blocked or faulty.

This isn’t a fix that can be done on a DIY basis. Your boiler repair company will need to take apart your boiler, and cleaning the burner, as well as removing any blockage in the jet. If a blockage was the issue, gas won’t be able to make its way into the burner, and the burner will lockout.

But, another common issue, is a heating pump problem. One of the most common issues with heating pumps, is a blockage in the form of heating sludge. Heating sludge is essentially, rust from the inside of towel rails, radiators and pipework; it can block all parts in your heating system, including the pump.

The blockage from the heating sludge restricts the circulation of water. When the PCB recognises this issue, it will lockout.

Your emergency heating repair company will need to remove any heating sludge blockages, checking for airlocks, ensuring the pump is on the correct speed setting, and is in all-round good condition.

In some instances, the pump will be beyond repair. Expect to pay around £250 for a replacement in these cases.

My Viessmann boiler is showing the 0C fault code, what does this mean?

The 0C fault code is shown on the Vitodens 100-W and the Vitodens 200. And, there are two things that could be causing the problem:

  • Electrical issues
  • Problem with the boiler’s ability to detect a flame signal.

If you suspect an electrical issue with your property (undervoltage, reverse polarity etc), you’ll need to speak to an emergency electrician. At EPHG Limited, we have both emergency electricians and emergency boiler engineers on hand to help. So, whatever the problem is, we’ll be able to get it fixed.

If the problem isn’t the electrics in your property, the most obvious place for your boiler engineer to start is the flame sensor. This might be signalling to the PCB that a flame is active, even when it isn’t. As the PCB is being led to think a flame is present when it shouldn’t be, it’s going to lockout the boiler.

Another potential cause of the problem could be the gas valve. Worn gas valves can stick. And, if the gas valve on your boiler is sticking partially open, this is going to lead to a flame being present, even when it shouldn’t be.

Gas valves that are sticking can be dangerous. If your boiler hasn’t already locked out, you should turn off your appliance and call a Gas Safe engineer as soon as possible.

Although your engineer can sometimes free the valve, a replacement may be needed if your gas valve is excessively worn. Expect the replacement cost to be in the region of £250-300.

How can the OF fault code be cleared from the display panel on my Viessmann boiler?

The OF fault code is an incredibly simple one to get fixed. The problem here, is your boiler needs a service.

A typical service should be under £100, and you should have one every single year. This is especially important if your boiler is still under warranty.

Most boiler manufacturers won’t honour their warranty, unless they see proof that the boiler has been serviced on an annual basis. And, that’s because a service can highlight potential problems, reducing the cost of long-term repair bills.

If you suspect you have problems besides the 0F fault, you should expect to pay extra to get them fixed. A boiler service isn’t inclusive of repair bills.

Most boiler servicing companies will complete little jobs alongside the service, such as cleaning out limescale and magnetic system filters, ensuring heating sludge doesn’t block up your boiler.

If the A4 fault code is displayed on the control panel, what does it mean?

It’s likely there’s a blockage in the system, meaning the pump can’t circulate water as efficiently as it should.

Your emergency boiler repair company will first start by checking that the pump isn’t airlocked. Airlocks are common in modern central heating systems. When they occur, they can act much like a blockage, causing water circulation to be reduced to a point where the PCB locks out the boiler.

The pump will need to be bled via the bleed screw and, it’s worth checking the pump for heating sludge blockages. Alongside airlocks, a heating sludge blockage could mean that the pump is overworked. This could lead to the pump wearing out prematurely and a new one being needed.

If you do need a new heating pump, you should expect to pay in the region of £250-300, from a leading brand such as a Grundfos, including all parts and labour.

My Viessmann boiler is showing the B2 error code, what is the problem?

The B2 fault code on Viessmann boilers relates to an internal electronics fault. You’ll need to call a Gas Safe engineer, who will then test all aspects of the electronics using a multi-meter. This helps them to pinpoint exactly where the problem stems from.

In a worst case scenario, the problem will stem from the boiler’s PCB. This component controls all other electrical components in your boiler. And, that means it’s one of the most expensive parts in a boiler to replace.

A typical PCB replacement could cost anywhere from £400 to £500, including parts and labour. The final price will depend on the exact PCB that your boiler uses.

But, your boiler engineer will also need to determine what’s caused the fault. In many cases, the B2 error code occurs simply due to old age. However, excessive boiler vibrations (from a worn pump or fan), or boiler leaks (from the pump or heat exchanger) could have caused the fault.

So, your boiler repair company won’t just need to fix the internal electrical fault, but also the issue that caused the fault to occur in the first place.

My boiler displays the B4 error code, is this cheap to fix?

The B4 error code relates to an internal fault, caused by a faulty PCB. On some occasions, the PCB can be fixed. This involves soldering loose connections back together and replacing sections of wiring.

And in some cases, it means reinserting the boiler chip card. The boiler chip card is the component that allows a boiler’s PCB to sync with the appliance. Most manufacturers create generic PCBs and get them to work with a range of different boilers, thanks to the boiler chip card. If this becomes loose, damaged, or isn’t the correct model for your boiler, a PCB fault will occur.

However, the PCB is a fragile electrical component, and it could need replacing. A replacement will cost £400-500 including parts and labour.

What does the CC fault code mean on Viessmann boilers?

If your boiler is displaying the CC fault code, it’s most likely that there’s an airlock or blockage in your central heating system. Both issues are going to reduce your boiler’s ability to circulate water. Eventually, the PCB is going to recognise that the flow and return water temperature differential is too great. Knowing there’s a problem, it will lockout.

The first thing your boiler engineer will need to do, is to remove any airlocks in the system. These can build-up in towel rails, radiators and even the heating pump.

After removing any airlocks, they’ll want to check that there aren’t any blockages. Typically, we find blockages causing the CC fault code to be displayed are due to limescale and heating sludge.

To remove the majority of limescale and heating sludge, your boiler engineer can run a hot flush. Once done, they can dose your system with central heating inhibitor; this helps to break down any heating sludge and limescale that builds-up in the system in the future.

With the sludge broken down, a magnetic system filter and limescale reducer can be fitted, preventing future blockages of this kind.

On some occasions, the circulation issue is due to a faulty pump. In these cases, a new pump will need to be fitted, costing around £250 including parts and labour.

What could cause the E4 fault code to be displayed on my Viessmann boiler?

The E4 fault code relates to a flame signal that is missing or weak. In both scenarios, the PCB recognises this as a potentially dangerous scenario, and locks out the boiler.

The PCB relies on the flame sensor to determine when the flame is present, and when it’s not. So, if the flame sensor is faulty, this is going to lead the PCB to be getting incorrect signals. Your boiler engineer can test the flame sensor using a multi-meter to determine if this is the case.

If both the flame sensor and the PCB test positive using a multi-meter, it’s likely there’s something restricting the flow of gas or air pressure.

Your boiler engineer will need to check the:

  • Condensate pipe and flue for blockages
  • The burner and jet for debris
  • Gas pressure to your appliance
  • Gas valve

Of all these components, the gas valve is the one they’re likely to focus on. The gas valve could be getting stuck partially closed, meaning the gas supply to the burner is restricted; causing a weak or non-existent flame.

My boiler is showing the EE fault code, what’s the most likely cause?

If the EE fault code is being displayed on your Viessmann boiler, the problem is a burner lockout. However, it’s most likely that the component causing the issue, is a faulty air pressure switch.

The air pressure switch on your boiler is incredibly important. It feeds back information to the PCB, letting the boiler know when the fan is operating, and it does this by monitoring air pressure.

The fan on your boiler vents harmful gases out of the flue. So, the PCB wants to see that the fan is operating alongside the burner. A fluctuation in air pressure might signify that the fan is running too slowly, or not at all. This would be dangerous, so the boiler locks out.

With the EE fault code, it’s likely the air pressure switch is faulty, and that means the readings it’s feeding back to the PCB are incorrect. Your boiler engineer can check the air pressure switch using a multi-meter to ensure that this is the case.

If the air pressure switch needs replacing, you should expect it to cost around £200.

If my boiler is showing the EF fault code, what could be the issue?

The EF error code on Viessmann boilers is like the EE fault code. The likely culprits are the burner, or the air pressure switch.

Your boiler repair company will want to dismantle your boiler and check the burner for blockages. It’s unlikely that a blockage is the case with a newer boiler, but carbon build-up over time, could cause a blockage in older boilers. They’ll be able to clean debris from the burner and jet, allowing your burner to operate more efficiently.

However, if the burner isn’t the cause of the error code being displayed, it’s likely the air pressure switch is to blame. Your boiler engineer will be able to test the air pressure switch for power, before deciding whether it needs to be replaced.

If the air pressure switch has no, low or intermittent power readings from a multi-meter test, it’s going to need to be replaced. Depending on your exact model of boiler, this is likely to cost around £200.

My boiler is showing the F0 error code, how can this be fixed?

The F0 fault code is one that relates to a blockage or circulation fault. This could be due to:

  • Airlocks
  • Blockages
  • Broken heating pump

Airlocks are the first place your heating company will start. They’ll remove airlocks from radiators and towel rails using a bleed key, and from the pump using the specifically designed bleed screw.

With airlocks free from the system, they’ll want to check that your system isn’t blocked full of heating sludge. So, they’ll run a hot flush to remove it, using specifically designed chemicals. If heating sludge is present, they may need to manually clean out the pump.

And, they’ll install some preventative measures to ensure this doesn’t happen again. This includes dosing the system with inhibitor, as well as fitting a limescale and magnetic system filter to remove any future sludge from your heating system.

If airlocks or heating sludge aren’t the issue, the problem is likely due to be with a circulation problem with the pump. After testing the pump using a multi-meter, it may need to be replaced. Expect a replacement pump to cost around £250 including parts and labour.

What does the F3 error code mean on Viessmann boilers?

If you’re seeing the F3 fault code on your Viessmann boiler’s display panel, it means the PCB can’t recognise the flame as being present.

It’s the flame sensor that tells the PCB when the flame is active, so this is the first thing for your engineer to check. If a flame is present but the PCB isn’t recognising it, it’s likely the flame sensor needs replacing.

However, if the flame sensor is operating correctly, your engineer needs to ensure that your boiler is getting enough gas. That means checking the gas pressure into the appliance, as well as ensuring the gas valve is operating correctly.

On many occasions, this is a simple case of the gas valve sticking. Your engineer may be able to stop the gas valve from sticking. However, for excessively worn valves, it’s likely they’re going to suggest a replacement. And, a typical replacement gas valve is going to cost around £300.

How can the F4 error code be fixed?

The F4 error code needs to be diagnosed in a similar way to the F3 fault code. The PCB isn’t recognising that a flame signal is present, and that’s causing the boiler to lockout.

They’ll need to check:

  • The flame sensor isn’t faulty, testing it with a multi-meter
  • Ensure the gas valve isn’t sticking, fitting a replacement if necessary
  • The gas pressure into your boiler is correct

My boiler is showing the F5 fault code, what is the problem?

The F5 fault code on Viessmann boilers relates to an issue with the gas supply. The gas pressure switch is showing that there’s a lack of pressure. Due to this being potentially dangerous, when the PCB gets this signal, it’s going to lockout your boiler.

Your boiler repair company is going to need to pinpoint the issue by checking:

  • The gas pressure switch isn’t providing incorrect readings
  • Gas pressure to your appliance is correct
  • The gas valve is moving freely

If my Viessmann boiler is showing the F6 fault code, what is the problem?

Like the F5 fault code, the problem here could relate to the gas pressure sensor, or gas pressure.

However, your boiler engineer will also want to check the fan. If the fan isn’t running at the right speed, or is faulty, the boiler is going to lockout. The lockout occurs in this case, as a safety precaution.

The fan takes harmful flue gases from the boiler, out of the flue. So, if it’s not working correctly, your boiler could be dangerous.

Your boiler repair company will want to test the fan using a multi-meter and ensure the speed setting is correct.

Is the F9 fault code an expensive one to fix?

Another common fault we see with Viessmann boilers, is the F9 error code. This code relates to the fan.

A boiler with fan problems is going to operate sporadically. And, that’s because the fan is a component that ensures your boiler is safe. The second your boiler gets the signal to say the fan isn’t working, it’s going to shut down; dangerous gases won’t be vented if the fan isn’t operational.

After testing the fan, your boiler engineer will be able to determine if they can fix the fan by securing connections and replacing sections of wiring, or if it needs to be replaced. If your boiler’s fan needs to be replaced, that’s going to cost around £250.

What does the FC fault code mean on my Viessmann boiler?

The FC fault code means your boiler has gone into fault mode. Typically, this is due to there being a problem with the gas valve. Testing the valve using a multi-meter will determine if this an electronic fault. However, on many occasions, the problem lies with a gas valve that’s sticking. Sometimes, your boiler engineer will be able to free the valve, rather than it having to be replaced.

But, the problem can also lie with the vent system being blocked. If this is the case, your boiler repair company will want to focus their attention on the fan. If the fans connections are loose, wires are damaged, or the unit is faulty, your boiler is going to lockout.

A fan that isn’t running correctly will lead to a boiler being dangerous. Harmful gases won’t be able to escape via the flue. So, if you see the FC fault code on your display panel, call an emergency boiler repair company as soon as possible to fix the problem.

What could cause the FE fault code to be displayed on my Viessmann boiler?

If your boiler is showing the FE fault code on the display panel, it’s likely the root cause is an issue with the PCB.

Typically, a boiler with a faulty PCB will have been acting sporadically prior to the FE fault code occurring. That’s going to mean it doesn’t respond to input from boiler controls, or cycles on and off at random. And, that’s because it’s the PCB that controls all components on your boiler. When the PCB is at fault, it can give or receive the wrong signals from other components in your boiler.

It’s rare that a PCB can be fixed. After testing the PCB using a multi-meter, it’s likely a replacement is going to be needed. Typically, you should expect a replacement PCB to be in the region of £400-500, depending on the model of boiler you own.

More importantly, your boiler engineer needs to determine what caused the problem. Besides old age, there are other things that can cause electrical components to fail, including water damage and excessive vibrations. Your engineer will need to fix/replace not just the PCB, but any problem that has led to the PCB damage in the first place.

If my Viessmann boiler shows the F-FA fault code, what’s the problem?

The F-FA fault code relates to a problem with the fan. When your fan develops a fault, it’s not longer able to vent harmful gases from your boiler, out of the flue. That means your appliance is potentially dangerous, so the boiler locks out until the problem has been found, fixed, and the boiler reset.

Your boiler repair company will check the fan to ensure that all wiring and connections are secure. In many cases, the 100A cable connected to the fan is the issue. This needs to be secured or replaced, depending on its condition.

Not all fan faults can be rectified. If the issue is with the fan itself, and not the connections/wiring, a replacement fan is going to be needed. If this is the case, you should expect to pay around £250 for a replacement.

My boiler is showing the F-FB fault code, what could be the issue?

The issue is again, with the fan. The fan hasn’t stopped when it should have, causing the boiler to recognise that there’s a fault. On many occasions, this issue can be fixed by replacing sections of wiring, or soldering connections.

Your boiler engineer will be able to test the fan using a multi-meter to determine whether it’s the whole component that needs replacing, or wiring/connections that are causing the issue. In some instances, replacing or repairing the 100A cable to the fan, is enough to fix the fault.

If the fan is showing lack of power after a multi-meter test, it’s going to need to be replaced.

What does the FR fault code mean on my Viessmann boiler?

The FR error on Viessmann boilers is usually connected to fan faults. Although old age is a killer of boiler components, it’s worth your boiler engineer checking to see if there’s any sign of water damage. And, they’ll want to do this to not just protect any repairs from future damage, but also to protect other boiler components too.

The most likely component to cause water damage on your boiler, is the pump. A quick visual inspection will usually help determine if the pump is leaking.

Typically, a pump leak will stem from blown seals. Like any seals, they degrade over time. Combine that will the excessive strain the boiler’s pump is put under during operation, and that’s going to lead to the pump’s seals leaking.

So, alongside fixing the fan fault, your boiler engineer will want to repair the pump. Most manufacturers provide spares kits, including seals. However, if your pump is beyond repair, a new one will need to be fitted.

A typical pump replacement for a Viessmann boiler will be in the region of £250.

Other boiler issues relating to other manufactures

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