Hello i have a potterton 28 performa boiler but iam having trouble with hot water flow.The central heating pressure holds fine and runs ,however i have to keep the water inlet tap turned off on the boiler or the release valve is activated.I can get hot water out of the taps by opening the hot tap on the bath,then partley open the water inlet tap on the boiler,if i open fully the pressure gauge just maxes out and the release valve is activated,i have already put a new release valve on but it still does not work.It appears some sort of pressure is building up in the hot water system some where,is there anyone who can help me?