I do sympathise with you... we also have the same model boiler with the same intermittent problem!
Apparently they are one of the most expensive and most reliable boilers - LOLl!
The only reliability with them is that every 12 - 24 months you HAVE to take out boiler insurance to cover the cost of replacing the diverter valve every time!!! I think these boilers were designed to keep the boiler engineers in a job!
We have previously had a BAXI and a WORCESTER boiler in our previous houses - with absolutely no problems at all. We moved into this house with a brand new boiler (the above mentioned Vaillant model) fitted not long before they put it up for sale and just after about a year of its life the problems began.
ANYONE READING THIS... DO NOT BUY A VAILLANT!
And just to finish... the clue of a diverter valve on the floor at your house is a very good clue, although looking at the installation manual (not the user manual) an f22 fault (which we keep getting) can also indicate a pump defect, pump lead defect or not enough water in the system.
Either way, be prepared to fork out a fortune every year for insurance - for parts that cost nowhere near that.
This is not a dig at what engineers charge but purely a dig at VAILLANT who designed and produced the piece of expensive trash!
sorry - had to get that off my chest!
MAY BE WORTH CALCULATING IF A CHANGE OF BOILER IS CHEAPER IN THE LONG RUN IF YOU PLAN TO STAY IN YOUR HOUSE FOR A LONG TIME AHEAD!? - I THINK WE MAY CONSIDER IT WHEN WE CAN AFFORD IT OR IF ANY SPECIAL DEALS COME UP.
Regards
i agree with you vaillant boilers are crap unrealiable,