I get noises from pipes particularly near the hot water tank in cupboard in bedroom, there are two what I believe to be motorized valve/switches at pipes in cupboard...noise sounds like water running through pipes, no apparent leakes. goes away when I put heating on. seems to only be when boiler for hot water is on. Vokera boiler, sealed , topped up if necessary, from main cold water feed. boiler in loft. system was drained for a new radiator last year and this is when noises noticed after refilling. could this be air in sysyem. tried draining and refilling couple of times but no change. is there somewhere in boiler or else where I could vent other than the usual - radiators.