7 Common Viessmann Boiler Problems and How to FIX Them

Viessmann manufacture some of the best and most reliable boilers on the market. But like any boiler, they can go wrong from time to time. So, if you have an issue with your Viessmann boiler, here is our short guide to the 7 seven most common problems, along with our top tips on how to resolve the issues.

There are a lot of different things that can go wrong with a boiler and while Viessmann boilers are among the most reliable on the market, even they can develop problems from time to time.

There are hundreds of different things that can go wrong with any boiler but in this guide, we will detail the 7 problems that we see Viessmann boilers developing most frequently. Even more importantly, we will tell you how to fix them too.

What to do if your Viessmann boiler is breaking down regularly

If you have an older Viessmann boiler that is now out of warranty and breaking down a lot, it might be time to invest in a new one. In the long-run, you could save money by buying a new one rather than continually fixing your old one.

For the best prices on high-quality boilers from Viessmann and all the other top manufacturers in the UK market right now, we recommend getting a quote from WARMZILLA.

WARMZILLA is an online installation company that offers some of the most competitive prices around, especially on Viessmann boilers. You can get a fixed price quote without sharing any personal information by visiting their website and filling in their quick online form.

There are lots of special deals, including extended warranties on some Viessmann models. You can even get your new boiler installed as quickly as the following day.

We always recommended readers get multiple quotes before investing in a new boiler. But we strongly recommend you make sure one of your quotes comes from Viessmann.

Top 7 problems with Viessmann Boilers – and how to fix them

In this section, we will outline the 7 most common problems with a Viessmann boiler and how to fix them. We can’t guarantee your boiler’s problem will be included, but there is a pretty decent chance it will be.

If you are in any doubt at all about your boiler, you should always get a qualified gas engineer to take a look for you. Boilers can be dangerous and you shouldn’t fiddle about with them if you don’t know what you are doing. Some of the fixes outlined below are things anyone can do, but others will require the help of a professional.

  1. Heating works but you have no hot water (or vice versa)

This is one of the most common problems with see with boilers manufactured by Viessmann and plenty of others. It is especially common on the Viessmann Vitodens 100 and Vitodens 200. There are a number of possible causes.

It could be down to a broken diverter valve. This is the component which directs hot water to the two different parts of your heating system. This valve can get stuck or break and end up directing all the hot water into one part of the system.

How to fix it:

If there is a problem with your diverter valve, you will need to replace it. Your heating engineer will be able to confirm the issue and quote for a new one. It is likely to cost in the region of £300-350.

If your boiler is quite old, your engineer might recommend replacing it. Ask them to check the other components to see if there are any other underlying issues that could cause future problems before you make your decision.

If you do opt for a new boiler, be sure to get several quotes, including one from WARMZILLA.

  1. Radiators Not Heating Up Properly

Radiators not heating up correctly is a common issue with all boilers and Viessmann ones are no exception. There are three ways this issue can play out:

  • Hot at the bottom but cold at the top – This is the most common issue we find and usually means there is a build-up of air in the radiator. This can be resolved by simply bleeding your radiators to remove the air from the system.
  • Hot at the top but cold at the bottom – This is likely to be caused by sludge in your central heating system that has built up at the bottom of your radiators. To clear this sludge, you will need to get a heating engineer to flush your system.
  • Radiators only half heating up – This problem suggests an issue with either your boilers temperature control or its water circulation system.

How to fix it:

The first two problems are simple to fix, as we have explained above. The third is complicated. It could be down to an issue with either the central heating pump or the flow and return temperature sensors.

You will need to get a qualified boiler engineer to come and assess the problem for you./ They will be able to check your pump for motor issues and leaks and also double-check your flow settings.

An engineer will also take a look at the NTC thermistors electrical current and resistance. This can sometimes cause the problem too, although it is less common.

If these aren’t working properly, it could be down to a fault or it could be caused by a build-up of limescale.

  1. A Blocked Burner

If there is an issue with your boiler’s burner, this is one you will definitely need the help of a qualified engineer for. This issue will most likely display an F1 error code on the display panel although some Viessmann models may show other error codes such as A3, B0, F-E1 and F-E2.

Your engineer will have to take quite a bit of your boiler apart to identify and fix the issue. It is often as a result of a flue gas sensor problem, but this is by no means the only cause.

How to fix it:

If the flue gas sensor is the problem, it will probably need replacing. This is not the most expensive fix on your boiler, but it is not the cheapest either.

If your boiler is old and out of warranty, you might want to consider taking a look at WARMZILLA to see if you would be better off spending your money on a new, more efficient boiler with a long warranty.

  1. Boiler Burner Lockout

If your Viessmann boiler has a burner lockout, this is usually caused by a blockage somewhere in your heating system. The most common error code for this is F2, although different Viessmann models could show E7, E8, E9, EA, EB, or EC.

The best place to start with this problem is actually your central heating pump, not your burner. This is something that can sometimes be fixed yourself but might well also require an engineer.

How to fix it:

When the burner in your boiler heats up the water, it is the job of the central heating pump to move this water around your system. But build-ups of sludge or air locks can cause the pump to fail.

Sometimes a blockage can be released by tapping the pump gently. But it is more likely you will need to either flush out your system or replace the pump and this will require an engineer’s assistance.

  1. Boiler Burner Broken

While a boiler burner lockout is likely to be caused by a blockage, the burner itself can sometimes go wrong too.

If the problem is with the burner, this will generate a different fault code. The precise code will depend on what the problem is and what model of boiler you have. For example, the Vitodens 200 is likely to display F10, F14, F3, or F4.

The most likely symptom of a burner fault is the absence of a flame, a weak flame, or a failure to recognise the flame.

How to fix it:

If there is a problem with your burner, you will need to get a qualified gas engineer to sort out the problem. The first thing they will check is whether the flame sensor is working or not. If this is the issue, a simple clean is sometimes all that is needed.

The burner itself might also need a clean if it has become blocked by debris from your heating system. This again could solve the problem.

If the sensor and the burner are both ok, the other thing your engineer will be checking will be the printed circuit board (PCB). This is the key component which helps the burner and flame sensor communicate with each other and the rest of the boiler. If the PCB isn’t working properly, the burner and sensor won’t either.

If there is a problem with the PCB, this could be expensive to fix. If you need a replacement, it could cost you £500+. If that is the case and you have an older boiler, you might want to consider investing in a new boiler from WARMZILLA. In the end, it could end up costing you less overall.

  1. The Boiler Won’t Fire Up

If you are finding that your Viessmann boiler won’t ignite, there could be a few different reasons.

It could be that the burner is blocked, as we discussed in the previous section. But it is more likely that this problem is as a result of a problem with the air pressure sensor.

How to fix it:

If the issue stems from the burner, you will need to get a gas engineer to check it out. With luck, all that will be needed is a good clean, and the problem will be fixed.

You will also need an engineer to inspect the air pressure sensor. If this has a problem, the boiler might think the pressure in the boiler is out when that isn’t actually the case. Any faults with the sensor itself or the wiring and the boiler won’t ignite.

You might need to replace the sensor or the wiring. In the worst-case scenario, you may need a whole new printed circuit board. As mentioned in the previous section, this is a big expense and if you have an older boiler, buying a whole new boiler might make more sense.

  1. Noisy Heating Pipes / Cold Return Pipe

If the central heating pump within your boiler is making noise, the most likely cause is actually a cold return pipe. If this is the issue, most Viessmann boilers will be showing an A8 fault code.

The two most likely causes of this fault are either an airlock or a build-up of debris in the pump. The good news is that both of these issues are easy to fix.

How to fix it:

You will again need an engineer, but this time all they will need to do is inspect the pump and clean it out. Assuming there is no more serious problem found, this should solve the problem and allow the flow settings to be altered to improve the water circulation.


Viessmann boilers are generally very reliable but even they can develop problems from time to time.

In this guide, we have highlighted seven of the most common problems we have encountered with Viessmann boilers and explained how to fix them.

Most of the fixes are fairly simple, but some are more serious and you might decide you are better off spending money on a whole new boiler. If you do, we recommended using WARMZILLA as they offer the best prices and some great deals on Viessmann boilers including exclusive ten-year extended warranties.

Have you had problems with your Viessmann boiler? What was the cause and how did you resolve it? Do you have any problems we haven’t covered in this guide? If so, please leave a comment below with your experiences or questions. We always try to respond to all readers’ comments.

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