Viessmann F5 Fault Code Causes & How To Fix The Boiler

James Elston
Written by James Elston
Updated on 17th May 2024
Posted on 16th May 2024
Viessmann F5 Fault Code Causes & How To Fix The Boiler

F5 Viessmann Fault Code Meaning and How to Fix the Boiler

The Viessmann F5 Fault code is related to the system’s gas pressure and electrical connections can also cause this issue.

Viessmann logo - Viessmann f4 fault code

So your Viessmann boiler is showing an F5 fault code? Don’t worry, fault codes don’t have to be frightening because even the highest-quality boilers will develop flaws as they age and our article will assist in answering any queries you have regarding your Viessmann boiler problem.

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F5 Fault Code on my Viessmann Boiler Meaning

Viessmann F5 Fault Code - get it checked by a gas safe registered engineer

This F5 fault code is defined by Viessmann, as “Air pressure switch faulty,” but could also relate to debris in the burner.

When you see the fault code on the combi boiler’s display panel, a boiler lockout will occur. These boilers are built to keep themselves safe and if this is the case then this lockout is in place as it will be dangerous if the boiler continues to operate.

Gas-related issues are extremely serious and therefore the lockout will remain in effect until the boiler engineer has resolved the issue therefore a Gas Safe boiler engineer will need to figure out and fix this problem and can usually be picked up on a Viessmann boiler service

If you possess a brand-new boiler made by Viessmann, the mixing damper option can then be thrown out, because Viessmann does not carry this component anymore.

The “air pressure switch” is a part of the electrical system, that calculates the pressure of the gas coming into the boiler and transmits the results to the Printed Circuit Board (PCB).

Before allowing the Viessmann boiler to proceed, every step of the heating process must be successfully completed safely, according to the PCB.

In order to prevent the system from operating in an unsafe manner, it would lock out and display a code like F5 if it receives a message from the switch indicating that the gas pressure is rather too low or too high.

A tiny metal flap known as a mixture damper closes the fan outlet by gravity and opens when the fan is operating and applying air pressure to it.

Starting the fan is one of the initial phases in the heating process, therefore if the PCB detects that this has not occurred for whatever reason, it will prohibit future stages from occurring.

The F5 failure code only applies to installations made before Viessmann discontinued this component in its boilers.

Viessmann F5 Fault Codes Causes

Problem with the Boiler’s Gas Supply

A gas pressure switch may not record adequate levels inside the boiler if there is an issue with the flow of gas from the main supply into the house.

Such problems are frequently caused by the gas metre regulator, which makes sure that the correct amount of gas has been flowing at all times.

Because these metres are frequently positioned outside, they might freeze in chilly weather, leaving them trapped at an inaccurate reading as well as stopping the flow of gas. If your metre is not shielded by a box, this is very probable.

The Gas Valve is Faulty

This valve is in charge of opening and closing to permit the proper flow into the unit after the gas has travelled through your house and reached the boiler.

Given enough use, the mechanism may start to stick because it is a mechanical instead of an electrical part.

In the case of the F5 error, it is more likely to be closed, but this is a problem whether it is fully open or closed completely.

The Gas Pressure Switch is Faulty

If the main supply of gas is entering the boiler normally, there could be an issue with the switch that measures internal gas pressure, and due to internal vibrations in the unit, the leads that connect this electrical component to the PCB may have broken loose.

The failure of these lines or the switch alone could also have caused the complete failure. The PCB will prevent additional gas from entering the unit if it is unable to read the switch to confirm that the gas pressure inside is safe.

With the help of this safety mechanism, excess gas in the boiler is kept from escaping which can cause damaging leaks inside the house if released.

Gas pressure is different to water pressure, so if you have low boiler pressure, check out our guide to get you repressurised right away.

Stuck Mixture Damper

On older devices that do have the F5 fault code, this flap is one of the most common causes even though it is not a standard on newer models. A rubber seal joins the flap to the outlet whenever the fan is not being used and over time the seal may eventually become really stuck so that even the fan’s pressure is insufficient to blow it clear because of damage, moisture exposure, or both.

PCB is Faulty

The PCB must control each electrical operation, so issues with it could easily prevent a boiler from carrying out its functions.

Localised damage can be brought on by loose connections or moisture seeping inside the device, therefore when it fails, it might have completely stopped functioning or be displaying a false error code.

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Should I Repair A F5 Fault Code On a Viessmann Boiler Myself?

No, you cannot. Any findings as well as repairs must be carried out by a certified Gas Safe engineer because they involve work inside the appliance and may interrupt the supply of gas.

How to Correct an F5 Fault Code in a Viessmann boiler?

In the event that the boiler’s gas supply is having issues:

Gas pressure can be measured at every step of the process, from the main supply towards the boiler unit, by a Gas Safe engineer.

A device called a manometer can be connected to the power source and provides measurements that can be compared to the acceptable level is sometimes used for this.

They will be able to thaw the frozen regulator if that is the cause and will almost certainly offer to prevent problems.

Two examples include enclosing the metre in a box and surrounding it with insulating materials. “Lagging” describes this situation.

An expert should be able to determine whether there is a problem with your gas provider even when there are no obvious issues with a component of your system.

If you have a Faulty Gas Valve:

When the boiler is tested, a clogged gas valve usually opens and closes improperly, making it easy to identify. In some cases, your engineer might be able to take the valve out and let it release before replacing it.

However, because sticking is frequently a reoccurring issue, it is typically more cost-effective to replace this element totally.

If your gas valve is beyond repair, you will need to replace it. A gas valve replacement should typically cost around £250, and the job should take about one day to complete.

Should a Mixture Damper become stuck in any way:

Even with Viessmann’s advice, there are various ways to deal with this problem because these parts are not included in newer installations.

While a few engineers might advise replacing the component entirely, others might advise splitting the rubber seal with a knife and leaving the flap in place to preserve the component’s functionality.

Ensure that the modification won’t affect your coverage or other Viessmann warranty unless the engineer advises completely removing the component, then your warranty will be affected.

The cost of labour will vary because accessing the part may necessitate time-consuming disassembly, but a fresh damper is typically less than £30.

Faulty PCB

If you have a faulty PCB due to the fact that all other potential causes have been overseen, a multimeter can be used by the engineer to test the PCB. This will demonstrate whether a particular connection or the entire part is malfunctioning and could cause you to have no hot water but the heating works.

Sometimes connections that are loose can be fixed without having to replace the entire component, but in the event of damage, a new PCB is needed. If moisture is the problem, they should search for any boiler leaks that might call for additional fixes.

One of the most expensive parts is the PCB, so replacing it should cost about £500.

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Can I restart my boiler to help solve the F5 fault code?

No, a reset will not solve the problem. The printed circuit board has recorded the fault code because it detects a gas supply or electrical problem. It will not work until the problem is repaired.

Because this is a dangerous fault, you should contact a Gas Safe registered boiler repair company right away. They will have engineers who will be able to diagnose the issue with your Viessmann boiler. And they’ll only restart the boiler after they’re certain the problem has been resolved.

My boiler stopped working when the F5 fault code is being shown

If a fault code appears on the display panel, your boiler has most likely stopped working; a Boiler not firing up is known as a lockout.

Boiler lockouts are intended to keep your boiler safe. In this case, the continued operation could render the boiler dangerous.

Gas-related issues are the most dangerous with any boiler. As a result, the lockout will remain in place until your boiler engineer has identified and corrected the problem, after which the appliance will be reset.

How does the gas valve on my Viessmann boiler work?

After passing through the metre, gas will proceed to the gas valve on your boiler. The gas valve communicates with the boiler to determine the amount of gas required, opening and closing as needed. This ensures that the burner always has the right amount of gas, increasing when you need hot water or heating and decreasing when you don’t.

Gas valves, like all mechanical and electrical components, can develop issues over time. That’s why we recommend an annual service.

If I need to replace my PCB, do I just replace my boiler?

Your boiler’s other parts are probably in good shape if it’s younger than five years old. So, although a replacement PCB might cost up to £500, this is the most economical choice.

But unless your boiler is older than this, or if internal components are in poor shape, replacement is an option. Obtaining quotes for a new boiler is advised if your boiler engineer believes any of the following components are in poor shape:

  • The heat exchanger
  • The fan
  • The pump

Choosing a new Viessmann boiler instead of repair?

Viessmann is a boiler manufacturer that is a family-owned and operated business that values quality and they are the largest boiler manufacturer in Europe. If you think that your old Viessmann boiler may have finally had its day then why not consider a boiler replacement?

Viessman boilers come in a variety of types, ranges and models – check out their range of boilers we sell online at Boiler central now:

Other Viessmann Troubleshooting Problems:

Some of the most common Viessmann Boiler Problems include:

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Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 16th May 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.

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