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Plog1976
Thanks for all your help on this. Got plumber coming today will mention about tanks in loft as nobody checked there yet
Nothing to do with pressure in taps, you have 2 x tanks in loft the small one keeps heating & hot water pipes toped up with water, if small tank runs dry water level in pipes will drop causing problems with circulation if you are able to access loft just check that small tank has water in it , if not ball valve will be stuck , sometimes just moving it up & down will free it up, if not you will need a new ball valve.