Generally, it means a lack of circulation, which may be caused by a lack of water in the boiler, an air in the boiler, a combined pump or other, undefined reasons that can be found during the boiler inspection by a service technician.
The F22 is a weak point of some Vaillant boilers. There are many reasons for this error to appear. Service technicians mostly blame water flow disruptions in what, but that's not it. I will mention the more important ones: - no water in the system (basic) - too low starting power of the boiler. (if nothing helps, you can raise a little - 1/4 turn of the nut) - disturbances in the electricity network (the highest probability of this error occurrence). These disruptions may be from the following devices - a hood fan, a gas stove igniter, a refrigerator lighting switch - opening or closing the refrigerator, fluorescent lamp starters (worse when there is a plant nearby using such hall lighting) - electrostatic charges (they can be from a human's hand - a charged one will touch the tap and the charges will go somewhere. They like to accumulate in the central heating network, like in a condenser, because in modern heating systems the central heating and ccw networks are usually not well grounded. - the boiler sensors are not making good contact
The Vaillant boiler is equipped with various very precise sensors and it is enough to disrupt their operation with some small electrical potential and we already have F22.
In my Vaillant, the F22 appeared more than a dozen times a month. No treatments of the blemishes helped. So I searched for a long time, and finally with such a pointer LAWO meter (the electronic one did not show) I was able to detect a small voltage appearing periodically between the gas pipe and the central heating supply pipe. It was enough to connect these pipes with a cable and the problem was gone. Electric spikes claim that it's not it, but so far, and it's been a few months, the F22 does not appear.
Just like a colleague wrote. I will add only one V. He was selling special mass cables that connected and fastened several elements, although that did not solve all the problems. As long as there is water and it can be seen on the pressure gauge, 95% of the problem is a matter of a malfunctioning power installation. These boilers require a relatively high (240V) and stable supply voltage, a wonderful solution was the board from the Hungarian version . (it had a built-in filter and voltage stabilizer, although I have only seen it once). Often the solution was to switch the power supply to a different phase, especially in old blocks of flats and tenement houses, where the load is very asymmetrical. In an extreme solution, the problem was solved by disconnecting the PE conductor from the boiler, but as we know it is not in line with the art. Bringing everything together should solve the problem, optionally look for an improvement in grounding the PE conductor. ps. VR-dialogue shows nothing in this case, it is a waste of time on trials.