Viessmann Boiler F3 Fault Code

The Viessmann fault code F3 relates to a flame that could be the lack of flame or no flame and here we have Q & A or require an engineer for an emergency boiler repair.

The Viessmann Boiler Fault Code F3 Error Common Q & A

Just below, we have a list of common questions relating to the F3 fault code on the Viessmann Boiler.

What does the F3 fault code mean on my Viessmann boiler?
How do I reset my boiler to fix the F3 fault code?
What could be the problem that’s causing my boiler to display the F3 fault code?
The flame sensor isn’t the problem, so what should my boiler engineer check next?
What does the flue have to do with the F3 fault code on my Viessmann boiler?
How can I check to see if my condensate pipe is blocked?
All the pipes are clear, what should my boiler repair company check next?
How could the spark generator cause the F3 fault code to be displayed?
How can the gas valve cause problems, and can it be easily fixed?
My boiler’s gas valve needs replacing, how much is this likely to cost?
My boiler repair company is saying I need to replace my PCB, does that sound right?

What does the F3 fault code mean on my Viessmann boiler

When your boiler’s printed circuit board (PCB) detects a problem, it will lock out and display a fault code. Continued operation would either be dangerous or could damage internal components. The fault code is displayed to make the fault-finding mission, easier for your engineer.

The F3 fault code on Viessmann boilers, relates to lack of flame. Either the flame isn’t being detected properly, or no flame is present.

Typically, we find this is common on the Vitodens 200. And according to Viessmann, the same problem could result in other fault codes being displayed, such as:

So, if any of these fault codes are being displayed, the problem is lack of flame, or no signal.

How do I reset my boiler to fix the F3 fault code

Fault codes on boilers, are there for a reason. You shouldn’t try and reset your boiler to try and clear the fault code. If you do and the boiler works, even for a few minutes, it could be dangerous. And even if it’s not, it could be damaging expensive internal components, leading to further repair bills.

What could be the problem that’s causing my boiler to display the F3 fault code

The first thing your boiler engineer needs to check, is the flame sensor. The flame sensor’s job is to pass on a signal to the boiler’s PCB, when a flame is active, and when it isn’t. In this case, the flame sensor is suggesting there’s no signal.

If your boiler engineer can see a flame in the burner, it’s likely that it’s the flame sensor that’s the issue. They can test the flame sensor for power, by using a multi-meter. And, if it is the problem, they’ll be able to replace it, and reset your boiler to fix the F3 fault code.

But, there are lots of other things your boiler engineer is going to need to check, if the flame sensor isn’t what’s causing the issue:

Gas pressure
Flue blockage
Condensate pipe blockage
Blockage in the burner
Spark generator fault
Gas valve adjustment and faults

If all that fails, they’ll need to test the PCB. The PCB gives and receives signals from all electronic components. So, if it fails, the boiler is going to work intermittently, or not at all.

The flame sensor isn’t the problem, so what should my boiler engineer check next

They’ll need to check everything that is connected to establishing and maintaining a flame in your boiler. And, that includes the gas pressure. If the boiler isn’t being provided with suitable gas pressure, then it’s not going to be able to establish a stable flame.

So, they can check the inlet pressure to the meter, and then to the boiler. Typically, the problem (especially when it’s cold), could be something simple, like the regulator on the gas meter freezing. If the meter freezes, the flow of gas to the boiler is going to be limited, or non-existent.

If your meter’s regulator has frozen over, it’s too exposed to the elements. To stop it happening again, it’s wise to get it boxed in, and then insulate whatever pipes are accessible.

What does the flue have to do with the F3 fault code on my Viessmann boiler

Your boiler needs to establish that two airways are free, before it operates; the flue and the condensate pipe. Without these two airways being free, harmful gases aren’t going to be able to escape from the boiler. And, that means that your appliance is potentially dangerous.

If you have a horizontal flue (that comes out of the wall), it’s rare that a flue blockage is going to be causing the issue. The only time this is the case, tends to be if the flue is old, collapsed, and therefore, blocked itself.

However, if you have a vertical flue (that comes out of the roof), it’s more likely that a blockage is causing the issue. Each vertical flue should be fitted with a flue guard. This stops debris from dropping in and blocking it.

If you don’t have a flue guard fitted, ask your engineer to check the flue for debris. If that’s the cause of the blockage, the problem can be fixed by cleaning out the flue and fitting a guard.

How can I check to see if my condensate pipe is blocked

A condensate blockage is more likely to happen in winter. Condensed gases are prone to freezing, and this is what causes the blockage. If it’s not ridiculously cold, then the problem is likely due to the fact the condensate pipe isn’t big enough, isn’t routed close to vertical, or isn’t lagged.

A boiler repair engineer will be able to not just thaw out the pipe, but check for all the above, putting preventative measures in place where necessary.

All the pipes are clear, what should my boiler repair company check next

The next thing your boiler repair company will want to check, is the state of the burner. It’s the burner that gives the boiler its flame. So, if there’s an issue there, that’s going to be the root cause of your problem.

Like many other parts of your Viessmann boiler, the burner can get blocked up. Your boiler engineer will be able to clean off any carbon deposits, so the burner works more efficiently.

However, it’s rare that carbon deposits on the burner, cause an issue. Instead, it’s the small jet that produces the flame, where the problem usually lies. As this jet is incredibly small, it doesn’t take much to block it. The tiniest piece of debris could block the jet, mean a flame can’t be established and that means your boiler is going to lock out and display the F3 fault code.

By carefully cleaning out the jet, your boiler engineer will then reset your boiler to clear the F3 fault code.

How could the spark generator cause the F3 fault code to be displayed

If your boiler isn’t producing a flame, it’s either gas or ignition related. If your spark generator isn’t working correctly, then that’s going to be enough for the F3 fault code to be displayed.

Your boiler engineer will be able to test the spark generator without any testing equipment. If it’s not generating a spark, it’s going to need to be replaced. Without a spark on the ignition, gas won’t be able to ignite to produce a flame.

How can the gas valve cause problems, and can it be easily fixed

The gas valve is what controls the flow of gas into the burner. Assuming the burner’s jet isn’t blocked, it’s down to the gas valve to open and close to provide the correct level of gas, based on your demand for heating and hot water.

The most common fault with gas valves on Viessmann boilers is that they stick. They can stick open (letting gas by, when they shouldn’t be) or closed (not letting gas by, when they should be).

As the F3 fault code relates to lack of gas or ignition, it’s likely to the gas valve is still partially closed, when it’s meant to be open.

Your heating engineer will be able to take apart the gas valve and check its operation. Most of the time, they’ll be able free the valve, so it operates correctly.

My boiler’s gas valve needs replacing, how much is this likely to cost

ot all gas valves can be repaired. If they have intermittent power (this can be tested, using a multi-meter), or they keep sticking, a replacement valve is going to be needed.

A typical gas valve replacement on a Viessmann boiler should be in the region of £250-300. That includes parts and labour, and the job should take around 1 working day.

My boiler repair company is saying I need to replace my PCB, does that sound right

Fault-finding on boilers can be extremely complicated, especially when it’s the PCB to blame. It’s the PCB that decides which fault code needs to be displayed. So, it stands to reason that if the PCB isn’t working correctly, the fault code being displayed could be wrong.

If your boiler engineer has tested to the PCB, and that’s the problem, you’ll need a replacement.

Before getting a replacement PCB, you’ll want to check expensive components such as the heat exchanger, pump, fan and gas valve. A PCB can cost upwards of £400 to replace. So, if other expensive parts are about to fail too, it would make more sense to invest in a new boiler.

Other Viessmann boiler issues

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

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