Viessmann F1 Fault Code Meaning, Causes & How To Fix It

James Elston
Written by James Elston
Updated on 22nd February 2024
Posted on 6th February 2024
viessmann f1 fault code

F1 Viessmann Fault Code Meaning and How to fix it

As much as Viessmann boilers are some of the most reliable on the market, as they get older errors and fault codes can occur.

Viessmann logo - Viessmann f4 fault code

The F1 Viessmann fault code relates to the flue gas temperature being too high.

Let’s take a look at what could be causing the Viessmann F1 Fault code and what it takes to fix the problem, but do be aware as this is a gas-related issue, only a qualified Gas Safe registered engineer can fix it, therefore this blog will help analyse the F1 fault code on your Viessmann boilers.

If you have an old boiler, it may be time to consider a boiler replacement as boilers over 10 years old quickly become less efficient and cost more in repair bills along the way.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

A boiler service is one of the main ways to prevent a Viessmann F1 error code and other cases of a boiler breakdown, book your boiler service here:

Book my service

What is a Viessmann F1 Fault Code?

From their website Viessmann defines the F1 Fault Code as “maximum flue gas temperature exceeded” and that the water pressure should be checked, the circulation pump checked and empty the central heating system of any air.

This means that a sensor in the flue pipe detected a temperature greater than what is recommended for safe boiler operation therefore this may be the cause of your Boiler not firing up.

This type of data is handled by the Printed Circuit Board (PCB), one of the internal components that serve the boiler’s control hub.

Before allowing the heating process to continue, the PCB validates that each stage has been completed successfully.

If there is something not right with the Viessmann boiler and the PCB detects this, then the boiler will lock out until it is fixed unless you have a PCB Fault which would cause even more problems.

It will then display an F1 Fault Code indicating what has to be repaired before the system can be restarted, if your boiler is starting to show fault codes, it may be time to consider a Look at Viessmann boiler service.

What Caused the Viessmann F1 Fault Code?

Fault Code DisplayedSystem FeaturesResultAction
F1 Error CodeFault CodeMaximum flue gas temperature exceededExamine the fill level of the heating system. Examine the circulatory pump. The system should be vented.

Faulty Pump

Because F1 indicates a circulation problem, it’s possible that the pump isn’t working properly. This is the primary component in charge of directing hot water away from the unit and into the pipes.

Viessmann F1 Fault Code - get it checked by a gas safe registered engineer

If it is unable to do so, hot water may become trapped in the boiler, resulting in overheating, therefore to fix this, the PCB must first recognise that the pump is operational before allowing the heating process to commence.

If you recently had a new gas boiler installed or a pump, the item may have been put at an incorrect angle.

If you have an old boiler, the pump may have failed or the bearings and shaft that allow it to spin may have been blocked.

Our Expert Gas Safe Engineer Says:

A faulty pump is not something that can be fixed by homeowners who aren't Gas Safe registered. With the F1 Viessmann fault you will likely need to call the manufacturer if your boiler is under warranty or an engineer if not.

James Murfin

Gas Safe Registered Heating Engineer

Air in the System

Air can enter the heating system gradually over time or in large volumes when maintenance such as bleeding radiators is performed.

It can form “locks” in pipelines or components like pumps, blocking the movement of moving parts and water and this can cause issues such as no hot water but the heating works.

Boiler Lost Pressure

Check the pressure in your boiler; if it is normal, this suggests a possible pressure sensor malfunction. If there’s low pressure in your boiler, increase the pressure and reset your Viessmann boiler.

If the boiler pressure continues to fall and the F1 Fault Code is shown, this suggests a possible leak somewhere in the heating system. Consider a visual check for the leak and/or get the assistance of a Gas Safe engineer to assist you in repairing it.

This is the most general reason for the F1 Fault Code and does not necessarily indicate that you have a serious cost problem to deal with.

The force required for hot water to circulate around the heating system at an optimum rate is referred to as boiler pressure.

Water Pressure

This is distinct from “water pressure,” these common faults are used to refer to the amount of water pressure required for water to flow from the taps. The heat produced by the boiler’s fuel combustion is meant to raise the temperature of a specific amount of water.

If there is less water running through the boiler due to low pressure, the surplus heat might travel to the surrounding components, causing overheating, however, if there is high pressure in your boiler, make sure that you release this too.

By looking at the pressure gauge dial, you can check the pressure in your boiler.

On combi boilers and system boilers, the gauge is usually at the form of the boiler so it is easy to see. The gauge on a heat-only boiler is often situated on the pipes directly underneath the boiler.

This displays the boiler pressure in bar units.

While your boiler is off and the water in the system is cold, most boilers should be at a recommended pressure range of 1 to 1.5 bar and this can exceed 1.8 bar when the central heating system is heated.

However, Viessmann boilers somewhat different range of 0.5 to 1 bar when the central heating system is cold and 1 to 1.5 bar when the boiler is hot.

Regardless, if your pressure gauge displays less than 1 bar, even on Viessmann boilers, the F1 failure was most likely caused by low pressure.

Boiler pressure decreases can occur without an underlying condition, and one or two drops are common each year. However, if the fall was rapid or remained intermittently after repressurising, another underlying issue is very probably present.

Faulty Flue Gas Sensor

If the sensor that supplied the high-temperature signal is defective, there may be no overheating at all. This little electrical component is called a thermistor.

This is due to the fact that when the temperature varies, the resistance in the boiler will vary, therefore making sure that temperature measurements are within the safe operating range.

The NTC thermoistor can wear over time like any part of a Viessmann boiler therefore causing it not to work properly and give false reading to the PCB.

Can I Fix my Own Viessmann Boiler with an F1 Fault Code?

Any mistakes you do to the boiler can cause significant damage to its life. We recommend the work of a professional gas-safe engineer.

If the boiler has lost pressure, you may be able to repressurise a Viessmann boiler and solve the problem yourself. However, we recommend you contact the work of a Gas Safe engineer to help you with the problem.

The boiler pressure will most likely get lower over time so it is not uncommon to see this F1 fault code. In most circumstances, you can repressurize your boiler yourself, extending its life and preventing damage to the boiler which can cause expensive repairs from overheated parts.

To repressurize your boiler, locate two taps linked by a short piece of piping beneath the unit which is referred to as the filling loop.

The tap handles will protrude from each pipe at a 90° angle, indicating that they are closed, and now that you’ve discovered this loop, you may perform the following:

  1. Turn off the boiler and check that it is cool.
  2. Turn the handles of both taps until they are parallel with the pipe.
  3. Watch the pressure gauge rise
  4. When the gauge achieves the desired bar reading, return both taps to their original positions
  5. Turn on the boiler

Once started, the boiler should maintain the new pressure level, therefore if this was the source of the F1 Fault Code, the error code should be removed from the display screen once the machine is reset.

Read more on How to Repressurise a Viessmann boiler

How to Fix a Viessmann F1 Fault code

If you have a boiler problem that includes removing the boiler cover or means amending the boiler with the gas supply attached, this requires the services of a licenced Gas Safe engineer.

This implies that if you have repressurised your Viessmann boiler and the system clears the F1 fault code from the screen, you’ll need to hire a professional to to attend your property and see what is exactly wrong with your boiler.

The time and expenses connected with these fault codes vary and it is always worth checking if your Viessmann boiler warranty is still valid or not as they may be able to fix your boiler for free.

Boiler Still Losing Pressure after you Repressurised it

If you have repressurised your boiler but your boiler is not working or the pressure keeps dropping your will want to inspect the system for leaks as this is the most common reason and even little breaches can cause pressure loss which leads to bigger problems.

Low boiler pressure can cause more problems too as well as make your boiler inefficient and the cost of fixing a leak will depend on the time finding the leak, how long it takes to fix the leak as well as the cost of replacement parts.

Viessmann pump fault

A registered gas-safe engineer should be able to determine the problem with a visual inspection if it is caused by a poorly placed pump.

If the pump is poorly installed then it can simply be reinstalled properly, however, if the shaft and or other parts such as bearings have been damaged, or the item has completely failed, they will most likely recommend a pump replacement.

This is often less expensive than attempting fix the pump, however, a central heating pump costs a considerable amount as parts are pricey.

The cost may vary a little depending on the model of your boiler, but expect a pump replacement to cost around £200-£300.

When There is Air in the System

The amount of effort necessary to fix an air lock will vary depending on where the air lock is and has been stuck.

An air lock in the central heating pump will necessitate the removal of the part before a bleed screw is used to let out the air similar to radiators until water begins to flow out, and once this is done, the pump may then be reinstalled, and circulation should resume.

Air in the internal circulation pump or failure to meet the minimum flow rate If the error notice persists, shut down the system.

The air within the pipes may be more difficult to detect, but if an engineer suspects this is the case, they can bleed the whole central heating system to remove any air and ensure that the water can flow properly around the system.

Flue Gas Sensor is Faulty

An engineer can look at the Flue Gas Temperature Sensor and test the electrical components with whats is known as a multimeter which measures resistance.

Any damage to an NTC thermistor would almost certainly necessitate a complete replacement, but thankfully these are reasonably affordable components, costing from £30-120 make and model dependant.

If the damage indicates the presence of other issues such as leaks or other damage caused by water then your Gas Safe heating engineer should be able to diagnose why this issue was caused in the first place.

This may result in additional maintenance and parts expenditures, especially if bigger components such as the heat exchanger are faulty.

Other Viessmann Troubleshooting Problems:

Some of the most common Viessmann Boiler Problems include:

When Is It Time To Replace Your Viessmann Boiler?

viessmann vitodens 050-w

The average boiler has a lifetime of 10-15 years. However, if you need to hire an engineer on a frequent basis, a new boiler may be a better option.

Other indicators that a replacement is required include noisy boilers or radiators, as well as leakage. Even the best combi boiler will fail one day.

Because older, less efficient boilers have higher energy costs, a replacement may not cost much extra during its lifetime.

See the latest Viessmann boilers available at Boiler Central right now and get a fixed price quote online in 20 seconds:

Viessmann boilers come in a variety of types, ranges and models – check out the:

Can a Power Flush Cause an F1 Fault Code?

If you recently paid for a power flush and are now experiencing an F1 Fault Code, there is a strong chance that the power flush is to blame. This is due to the fact that the power flush can shift material in your heating system, and if the debris is linked to corroded piping, it might eventually create a leak in your central heating system.

How to keep your Viessmann boiler from breaking down in the future:

Regular boiler service is the best way to avoid costly, inconvenient, and even dangerous boiler faults in most cases. In fact, you should have all gas appliances in your home safely checked and serviced on an annual basis by a Gas safe engineer. See our boiler service price and costs guide here and also book your service online with Boiler Central now.

Why wait and watch your boiler break down? We provide boiler cover with free annual boiler servicing, so you can stop the worry and let us assist you and check your boiler on a regular basis instead of making a yearly appointment.

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 6th February 2024

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

Broken boiler?

Get a replacement installed next-day. Free fitting and disposal of old boiler

Get my fixed price
Get a great price on a Which? Best Buy boiler online in 20 seconds
  • Over 15,000 boiler installed
  • Rated Excellent on Trustpilot
  • Fair, fixed and final prices
  • No pushy salespeople
  • Next-day installation
  • 0% deposit interest-free finance
Next-day fitting available until 2pmGet a quote now >