The F3 error code means that the boiler has detected that there is no flame present. This can happen if the boiler has ignited and gone out, hasn’t ignited at all, or the boiler hasn’t recognised the flame after ignition.
The Viessmann F3 error can be produced for many different reasons, including: a blocked flue, a faulty PCB, a faulty spark generator, faulty electrodes, faulty gas valve, faulty burner, poor earth connections, a blocked condensate pipe, and incorrect gas pressure.
If the flue of your boiler is blocked, your appliance will be unable to pull in fresh air for combustion. As we all know fire needs oxygen to burn, so no air = no flame and your boiler will display an F3 error code.
If the PCB, electrodes, or earth is faulty, your boiler might not be able to recognise the flame. When the burner ignites the electrodes pass a small AC current through the flame, the energy from the fire converts this current to a DC current, a process known as flame rectification.
If the electrodes are faulty they might not send this current to the PCB, or if the PCB is faulty it might not recognise the DC current and your boiler will display an F3 fault code. Similarly, if the earth connections are poor or corroded, there might be too much resistance, and the current will not reach the PCB, resulting in a Viessmann F3 error message.
If the burner, spark generator, gas valve, or gas pressures are faulty your boiler will not be able to complete the ignition process, and after 3-5 attempts it will lock out with the F3 error message.
After sufficient time has passed and the temperature difference between the flow and return has reduced, resetting your boiler will temporarily clear the F2 fault code.
Although the fault will clear, the boiler will probably still not work.
As the Viessmann F2 fault is usually caused by the pump either seizing, or due to the PCB not sending power, after the boiler has run through its ignition sequence your Viessmann boiler will quickly lockout out again to the F2 fault.
Similarly, if your system is severely blocked and the flow of water is restricted, the temperature of the flow and return pipes will increase too quickly and your boiler will again lockout with the F2 fault code.
It is very unlikely that you will be able to repair the Viessmann F3 fault yourself.
It will almost certainly need a Gas Safe registered heating engineer, because the fault will probably be with the PCB, and you will need to dismantle to boiler to replace the faulty part.
Some basic checks you can do are, check the flue outside – has something covered it, are bushes or trees obstructing the path for fresh combustion air? If you have any other gas appliances like a cooker, are these working? are you also having trouble with your drains or sink blocking? All of these could be the reason your boiler isn’t working.
For more things to check before calling a gas engineer, click here.
The Viessmann F3 error is quite a serious fault and will almost certainly need a professional to repair it.
There are some things you can check before you call us, but remember not to take the case off of the boiler.
Apart from being incredibly dangerous, you could do more damage and end up needing a new boiler instead of just a repair.
Heatsy are Viessmann trained, DBS cleared, and Trading Standard approved heating contractors. We specialise in domestic heating boiler repairs, Gas Safe number 648547.
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