Hi. Just wondering if anyone can help with a very noisy Vailant Turbomax 824E combi boiler. I have CH and hot water but when any hot water is being used the boiler makes a load moaning sound ( sounds a bit like a plane coming into land) for a few seconds then it stops for a few seconds and then moans again. This carries on until the hot water is turned off. In addition the water pressure keeps dropping although cannot see any leaks other than have noticed water coming from the overflow pipe outside. Any advise on what could be the problem would be great.