Vaillant powermax ?

Thought I would answer my own question after a visit from a nice man from Vaillant.

He checked the boiler and said all was fine - and so it should be with a four year old boiler! He said then that he would check the filter which is on the return pipe and behold it was chock full of gunk! A quick wash and clean up and put back. Hey presto a warm house!! It was preventing the water returning properly and the boiler couldn't cope.
Also caused the f22 problem - so if you have this problem, check the filter!

Hope this helps anyone else who has much of the same problem.

Alibutler
December 2008