Viessmann F0 Fault Code – Likely Causes, And Possible Fixes

October 17, 2022

What Is the Viessmann F0 fault?

The Viessmann F0 fault is a safety feature of the Viessmann boiler range, including the Vitodens 100 and 050 boilers.

It basically means the boiler has overheated and has in turn stopped itself from firing to prevent any further damage.


Common Causes of The F0 Fault

The F0 fault code on the Viessmann boiler can be caused by a blockage in the system or a pump failure. The blockage could be caused by corrosion (‘sludge’), or limescale blocking the pipes and restricting the flow of water.

If the pump has seized or is running slow, this too could cause the water temperature to rise too quickly and result in intermittent F0 faults.

Other common causes are airlocks and low water pressure. Both will cause your Viessmann boiler to overheat and result in an F0 fault.


If I reset my boiler, will this fix the F0 fault code?

The Viessmann F0 fault is classed as a volatile lockout, meaning you will need to manually reset the boiler to clear the fault.

If the problem was caused by an airlock, slow pump, or sludge in the pipes it is possible that the boiler will work for a while. But the fault will return, and it’s likely that running the boiler in this condition will cause more damage to your boiler, and heating system.

If the pump has failed completely, or the system pressure is at zero your boiler will probably attempt to fire again but will quickly overheat and lockout out with the F0 fault.


Can I Fix the F0 Fault Myself?

Sometimes. If the fault is due to low pressure, you can re-fill the boiler following the process in the user's instruction. If you don’t have the manual, you can find it here.

Likewise, if the fault is caused by air, you can fix the issue by bleeding the radiators, then following the process above to re-fill the boiler. To learn how to bleed your radiators, click here.

If the fault is more serious and caused by system corrosion or a faulty pump, you’ll need to call a Gas Safe registered heating company to arrange a boiler repair.

An annual boiler service can help to spot these issues before they turn into something more serious. A professional company will check the quality of the water in the heating system and may recommend some treatments before you need to have the system powerflushed, or worse, a new boiler installation if the main heat exchanger is completely blocked and corroded.



The F0 fault is an indication that you have an underlying issue, some more serious than others.

You can try to temporarily clear the fault by resetting the boiler but be warned this will usually lead to more damage in the long term.

Some issues can be fixed by yourself, some will need a Gas Safe registered heating company to complete a professional repair.

Heatsy are Viessmann trained, DBS cleared, and Trading Standard approved heating contractors. We specialize in domestic heating boiler repairs, Gas Safe number 648547.

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