prv may have grit in it, sometimes they activate and shut again or they keep leaking. if your pressure gauge is set to 1bar when ch off and then rises to 3bar when ch on you may need to get your expansion vessel checked it may need recharging. which will keep activating your prv, so i would get the vessel checked first then prv. you can check vessel yourself if you have a trye pressure gauge.
hi-spec plumbing
March 2007