Vaillant error F22

SOURCE: vaillant Boiler time switch no user manual

http://www.vaillant.co.uk/stepone2/data/downloads/9a/42/00/timeSWITCH_120.pdf

SOURCE: f22 on my vaillant boiler turbo max

Hi Guy's,
The answer is that your system is out of water pressure.
Usually there is a nob on the right under the base of the unit near to the small dial to the right of the front cover.
To enable the system to work correctly the needle on this dial should be in the Grey, about midway position.
Currently with fault F22 this will be lower to below the Grey and on the needle.
To bring the pressure back to the correct position, you need to turn this nob until you hear the water entering the system, KEEP AN EYE ON THE DIAL AND TURN THE WATER OFF AGAIN WITH THIS NOB ONCE THE DIAL IS IN THE CORRECT GREY POSITION AS MENTIONED ABOVE. DO NOT OVER FILL THE SYSTEM. I suggest you check this every six months or so.
Once this is corrected your unit will light up again.
Best of luck. Mike. N.