pressure keeps dropping on combi boiler?

my parents recently had a vaillant combi boiler fitted in their loft (as advised by plumber)but the pressue gauge as dropped several times already,leaving them with out any hot water,central heating or both & my mum who's in her late 60's keeps having to climb into the loft & turn certain taps/valves to rectify the problem.i cringe at the thought of my mum having to do this but she's very independent,surely either "vaillant" or the fitter could come up with a better solution,i'd go ape if i had to keep messing about like that,plus it's just not reliable,can you suggest a solution please?