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Common Viessmann Boiler Problems


The Viessmann Group was created in 1917 in Germany. Today, they are one of the leading providers of heating solutions in the world. Viessmann operates in more than 74 countries and has over 12 offices and 12,000 employees. In addition to providing heating solutions, they also come up with renewable technology.

With that said, your Viessmann boiler in the recent past has been breaking down a little too often. And though you fix the heating problems, lockouts, and overheating, you wish there was a way to diagnose the problems earlier or, better yet, prevent these breakdowns.

Well, Viessmann boilers have fault codes designed to make boiler diagnosis easier. We also recommend regular boiler maintenance for early detection of problems before they develop into major inconveniences.

In this piece, we share some common Viessmann boiler problems along with their faults and quick fixes.

No hot water but the heating works

If the boiler heating is working correctly but there’s no hot water, there are several causes. This specific problem is common with the Viessmann Vitodens 200 and Vitodens 200.

And though there are lots of causes, the Gas Safe engineer might diagnose a faulty diverter valve. Boiler diverter valves are designed to switch between heating and hot water functions. And without the diverter valve, the radiators would overheat every time you turned on a hot water tap and shower.

But in this case, the diverter valve is stuck on heating.


If the boiler is old, there’s a chance the diverter valve cannot be repaired. In this case, replacing the boiler is a good option (especially if other parts are close to failing).

A new diverter valve costs about £250, including labour.

Radiators only heat halfway

There are three ways this problem can manifest.

Radiators are only heating the rooms halfway: this is a boiler fault problem. Usually, it’s a problem with water circulation or temperature control.

Radiators are hot at the top and cold at the bottom: this cause of this problem isn’t related to the boiler. Instead, it results from sludge build up in the central heating system. The sludge blocks water from getting to the bottom.

Radiators are cold at the bottom and hot at the top: this usually means there’s an airlock in the system. Bleed the radiators to remove excess air in the system. All you need is a bleed key to open the valve until all air has escaped. Reinstate pressure by topping up water.


Assuming the radiators are half heated, you should check for:

  • Pump faults
  • NTC thermistor fault

A Gas Safe engineer will check the pump for leaks, correct flow setting, and a seized motor. They will then use a multi-meter to check the electric current flowing through the NTC thermistor. If the thermistors are faulty they’ll be replaced.

Limescale build-up can cause incorrect temperature readings. It causes the region close to the thermistor have higher temperatures resulting in wrong signals premature boiler shutdown.

Burner blocked

Burner faults are difficult to diagnose without a Gas Safe engineer checking under the hood. An F1 boiler fault often accompanies this problem. Other Viessmann boiler models display A3, B0, F-E2, and F-E2.

A faulty flue gas sensor often causes the problem.


The common fix involves inspecting the flue sensor. If it’s faulty, it’s replaced. However, if the boiler is out of warranty and other parts are failing as well, we advise investing in a new boiler.

Burner lockout

This is a boiler fault that will not give you a specific hint of what is a miss. However, the most common fault code is F2. But in old Viessmann boilers like the Vitocrossal 200, other boiler errors displayed include E7, E1, E9, E8, EA, EC, EB, and F2.

Usually, these fault codes point to a block in the system. The easiest diagnosis is a faulty central heating pump.


A circulation fault makes the burner lockout. But usually, it’s not a faulty burner.

When the burner is heating water, it needs help to pump and circulate it to the house. If this doesn’t happen, the boiler overheats. The most common cause is an airlock.

You can bleed the system to get rid of excess air. You don’t need a Gas Safe engineer for this.

Faulty Burner

If you have a faulty burner on your hands, you might see any of the following fault codes: F-B7, F-F2, F-F4, F-F7, F-F9, and F-F8. In the Viessmann Vitodens 200, you’ll get error codes, including F4, F3, F14, and F10.

The most common cause of boiler lockout is no flame signal, absence of a flame, or a weak flame.


A Gas Safe engineer will inspect the flame sensor. Usually, it needs cleaning. If it’s in good condition, they will check the burner for blockage. But if it’s not blocked, then it’s broken.

If the flame sensor and burner are working correctly, the engineer will have to inspect the PCB. The PCB communicates with the burner and sensor.

If the PCB is broken, the two will not work correctly. If you don’t have a boiler warranty and the repair bill is expensive, we recommend getting a new boiler. With a new boiler, you benefit from improved efficiency, and it’s cheaper in the long run.

Cold return pipes of noisy pump

If the heating pump makes noises, there’s a high chance the return pipes are also cold. In this case, the boiler might display an A8 fault code.

The noises and cold return pipe mean the heating pump is blocked by debris or there’s an airlock. Luckily, the two are easy to fix. The boiler monitors water circulation. If the minimum flow rate isn’t achieved, the boiler will lockout.


The heating pump should be cleaning and inspected for damage. If the boiler is working correctly, the flow settings should be adjusted to boost water circulation and meet minimum flow rate requirements.

The boiler doesn’t fire up

If the boiler doesn’t ignite, there are several causes.

It could be a faulty or blocked burner. A blocked burner yields an F5 error code. However, it could also be a problem with the air pressure sensor.


First, the burner should be inspected and cleaned. If this doesn’t clear the fault code, the Gas Safe engineer will inspect the air pressure sensor. The sensor tells the PCB that the air pressure is normal.

But if there’s a fault with the sensor, wiring or circuit board, the boiler will not ignite. This could mean you need to buy a new sensor, replace the PCB, or repair the wiring. However, if the boiler is old and out of warranty, don’t waste your money on repairs – invest in a new boiler.

Anything more than £500 makes sense to invest in a new boiler.

Frozen condensate pipe

With the new Viessmann Condensing boiler, some waste gas produced by boilers cool to water as they drain to the main drainage system through condensate pipes. A block in the condensate pipe causes a boiler lockout.

The condensate pipe is prone to freezing and blocks during winter. The block causes an F4EE fault code. Luckily, this is an easy problem to fix.


You can fix this problem without hiring a Gas Safe engineer. Thawing a condensate pipe is easy. Pour hot water over the frozen spot or hold a bottle of hot water over the block. Do not pour hot water over the condensate pipe as it will melt the pipe.

Low boiler pressure

Viessmann boilers operate under specific boiler pressures. Too low boiler pressures result in a strain in the heating system and potential damage to all boiler parts. The standard boiler pressure range is between 1 bar and 1.5 bar. When the boiler is operational, the pressure might increase to 2 bar.

Luckily, solving this problem is easy.


The quick fix involves increasing pressure within the boiler system. Repressurizing a boiler pressure means adding water to the system. As you add water through the external filling loop, keep an eye on the pressure gauge. Stop when the pressure gauge pointer is safely between 1 and 1.5 bar.

Next, reset the boiler to clear the error code.

Boiler leaking

Often, low boiler pressure is caused by a leak in the system. If you add water to the system and the pressure suddenly drops, it signifies a leak in the system.

The leak could be in the piping or inside the system on the boiler joints. If you see an unexplained pool of water in the house, this is the probable cause. You should fix the problem as soon as possible lest it causes corrosion, rust, and a breakdown of electrical components.


If you can locate the leak on the pipe, you can tighten or replace the joint. However, if the leak is internal, you should call a Gas Safe engineer for diagnosis and a fix.

Other boiler faults codes and troubleshooting

Fault code FE: Faulty PCB

How to fix: Replace the PCB. If the boiler is out of warranty, install a new boiler.

Fault code F-FA: Faulty Fan

How to fix: Replace or tighten wiring and connections or replace the faulty fan.

Fault code FC: Faulty gas valve

How to fix: Free the gas valve or replace it.

Fault code CC: Airlock in the system

How to fix: Bleed the radiator.

How to improve your boiler’s life

Viessmann boiler guarantee

Viessmann boilers come with a standard 5-year warranty. The warranty covers material or manufacturing defects. These materials and parts are only those manufactured by Viessmann. The warranty does not cover corrosion or sludge build-up.

To get the warranty and maintain it, you need to register the boiler on the Viessmann website within 30 days of installation and service it annually, respectively. Luckily, Gas Safe engineers do the registration for you after the installation.

Viessmann boiler cover

Once the standard boiler warranty expires, you should consider buying insurance. The insurance serves as a warranty. The only difference is that you will pay premiums. Before choosing the best insurance for your boiler, consider the annual service and safety inspection they offer. And though you can take the insurance with Viessmann, you are not obligated to do so.

Viessmann boiler service

To get the best performance and life from your Viessmann boiler, you should conduct regular servicing and maintenance. At the least, you should conduct an annual service as required under the warranty regulations.

After the servicing, the engineer will offer you a certificate as proof to present it to your insurer if the need arises. The annual boiler service is also important for:

  • Maintaining safety
  • Preventing boiler breakdowns
  • Keeping the energy bills low

If you see any of the above fault codes, you now know what to do. If the fix isn’t a DIY, always hire a registered Gas Safe engineer. They will ensure safety and prevent further damage.

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