Vaillant Ecotec Pro with F22 fault?

Vaillant Ecotec Pro with F22 fault - I know this means it needs topping up with water as the pressure is .2 bar. Read all the answers I've found on the net BUT - don't have 2 white handles to turn, there are no valves to turn on the ends of the bendy silver pipe and can't see any other valve that are closed. If I could see a closed valve I'd open it and listen for water and watch the guage. HEEELLLLPPP!!!