have had to remove central heating units to lay new floor .When put back there was no water pressure shown on the Vailant hot water unit and an f 13 fault showed up.I have water from both the hot and cold taps but no hot water from the hot tap.What do I have to do to regain a pressure reading on my Vaillant system.There is gas in the system as I can hear the gas burner however it shuts down within minutes as there is no water pressure.
What do I have to do to rectify this problem.

Fred Grimminck, June 2008

you need to top up the system via the filling loop situated underneath the boiler, there should be a slotted lever key fitted into a 1/4 turn valve there are 2 of these valves, you need to open both Not too easy to describe but have a look in instruction manual. it needs only to be topped up to around 1 bar

Ian t, June 2008