Viessmann Boiler F4 Fault Code
The Viessmann fault code F4 related a lack of flame detection and here we have Q & A or require an engineer for an emergency boiler repair.
The Viessmann Boiler Fault Code F4 Error Common Q & A
Just below, we have a list of common questions relating to the F4 fault code on the Viessmann Boiler.
- What does the F4 fault code mean on my Viessmann boiler?
- What are the likely causes of the F4 fault code being displayed?
- Is this a boiler fault that can be fixed on a DIY basis?
- What will my boiler engineer be looking for in the electronics?
- If there are problems with the ignition lead or spark generator, what will happen?
- My boiler engineer thinks the burner might be to blame, how is this possible?
- How can the flame sensor contribute to no flame being detected on ignition?
- What does the gas valve have to do with a flame detection fault?
- If I need a new gas valve, how much is it likely to cost?
- My boiler engineer thinks the PCB could be to blame, is this possible?
- How much is it going to cost to replace the PCB on my Viessmann boiler?
What does the F4 fault code mean on my Viessmann boiler
If you’re seeing the F4 fault code being displayed on your Viessmann boiler, the problem lies with lack of flame detection.
When you demand for hot water or heating, your boiler gives the signal to all relevant parts. That includes the likes of the gas valve to open, and the burner to fire up. In this case, no flame is being detected in the burner, which means hot water and heating isn’t going to increase in temperature.
Alongside the F4 fault code, it’s likely the boiler will lock out. In most instances, this is to make sure the boiler isn’t dangerous. But, in other instances, the lock out is put into place to ensure that further damage isn’t caused to boiler components.
What are the likely causes of the F4 fault code being displayed
After calling a Gas Safe boiler repair company, they’ll get to work fixing your boiler. They’ll be looking to analyse anything that could interfere with your boiler producing a flame. And, that’s going to include checking the:
- Electronics
- Ignition lead
- Spark generator
- Burner
- Flame sensor
- Gas valve
- PCB
Is this a boiler fault that can be fixed on a DIY basis
There are very few boiler faults that can be fixed on a DIY basis, and this certainly isn’t one of them. And, you also shouldn’t try and reset your boiler. The reset function that is integrated into modern boilers, is designed to be used when the problem has been rectified; it’s not a way to fix that problem.
To fix the fault, your engineer will need to test various parts, as well as taking your boiler apart. The only people allowed to work on Gas boilers, are Gas Safe engineers. So, we’d suggest getting hold of a Gas Safe boiler repair company as soon as possible.
What will my boiler engineer be looking for in the electronics
The first thing your boiler engineer will want to do, is give the internals of your boiler a quick visual inspection. This can quickly highlight any issues with water damage, or general damage to wires and connections. In some cases, minor damage can be rectified.
Alongside connections being secured, wiring repairs could be enough to get your boiler up and running again, and a reset will clear the F4 fault code on your boiler.
Visual inspections won’t always highlight potential problems. For this reason, your boiler engineer will want to test the most important sections of the electronic circuit using a multi-meter. This will help them pin-point where the exact problem lies.
If there are problems with the ignition lead or spark generator, what will happen
The ignition lead and spark generator are integral parts of the ignition system in your boiler. If they are faulty, then no spark will be created, no flame will be present, and that can cause the F4 fault code to be displayed.
Your boiler engineer won’t just want to test these components for power, they’ll be looking for signs of moisture. Even the smallest amount of moisture on the spark generator or ignition lead is going to cause both units to fail.
My boiler engineer thinks the burner might be to blame, how is this possible
The burner is the component that helps not just to establish a flame, but to maintain a flame. Over time, carbon can build-up in the burner, causing small blockages. This is most likely to cause a fluctuation in flame signal, rather than not allowing a flame to be present.
When a flame isn’t present, your engineer will want to focus their attention on the jet in the burner. These tiny jets supply gas to the burner. Being so small, they can get blocked up incredibly easily. Even the smallest amount of carbon debris in the jet, can cause a flame not to be established.
It’s unlikely the burner and jet need to be replaced. Instead, your boiler engineer will need to remove the jet, clean it and then refit it. If there is a steady gas supply after installing the jet, the boiler can be reset to clear the F4 fault code on your boiler.
How can the flame sensor contribute to no flame being detected on ignition
Your boiler has a range of sensors. For example, there are sensors monitoring water temperature, water pressure, air pressure, and the flame sensor, which monitors the flame in your boiler.
After you call for heat, your boiler fires up the fan to create a draft; this expels gases via the flue. Once this is operational, gas is let into the burner via the jet and ignites. At this point, the printed circuit board (PCB) wants to see a signal from the flame sensor, that a flame is present.
If the flame sensor is faulty, it won’t give the signal to the PCB that the flame is present. Whether it’s present or not, the boiler is going to lock out and display the F4 fault code.
So, your boiler engineer will need to inspect and test the flame signal. If they determine the flame sensor is getting no, or intermittent power, they’ll need to replace it.
What does the gas valve have to do with a flame detection fault
As we mentioned above, the gas valve lets gas into the burner when heat is called for. But, gas valves are mechanical parts and can wear over time. On many occasions, we find that gas valves are sticking.
Sometimes, this means that gas is being allowed into the burner when it shouldn’t be, due to the gas valve being stuck partially open. This is called “letting-by”.
In the case of the F4 fault code, it’s more likely that the gas valve is stuck closed, when it should be open. That means it’s not able to feed gas via the jet and into the burner. Ultimately, that leads to not flame being produced, and a flame detection fault.
Your boiler engineer will need to check the electronics on the gas valve, and free it from sticking. If the valve isn’t in perfect condition, it’s likely the boiler repair company you use is going to suggest having a replacement gas valve fitted.
If I need a new gas valve, how much is it likely to cost
A gas valve replacement for a Viessmann boiler is likely to cost around £250-300 and take one day to fit. After replacing the valve and resetting the boiler, the F4 fault code should be cleared from the user interface.
My boiler engineer thinks the PCB could be to blame, is this possible
The PCB gives and receives signals from the electrical components in your boiler. That includes everything mentioned above, from the gas valve, through to the flame sensor.
If there’s a problem with the PCB, then a few things will occur. Firstly, you’ll notice that your boiler works intermittently. This might mean it cycles on and off at random or doesn’t respond from commands on the user interface (turning up hot water temperature for instance).
More importantly, it might be that the signals that it’s getting from boiler components are intermittent, or non-existent. And, this could mean that signals such as the flame sensor’s signal to say a flame is present, isn’t being pushed through to the PCB.
On some occasions, the fix is as simple as securing wires and connections. In a worse case scenario, the PCB will need to be replaced.
How much is it going to cost to replace the PCB on my Viessmann boiler
If a PCB replacement is the only way to clear the F4 fault code on your boiler, you should expect to pay somewhere in the region of £400-500 including parts and labour.
Other Viessmann boiler issues
For more boiler issues regarding the Viessmann Boiler then please visit the Ideal Boiler Problems And Cures page.