Hi I have a problem that is sof a mystery.. a few days ago we decided to fill up a 2 seat theraputic bath in our bedroom in the basement, we have not used in in a few months, as soon as the hot water was turned on a loud knock came from the ceiling/wall then the hot water stopped, in fact there was no hot water comming out from the entire house. since the tank is a rental I called the gas company, he came, said it was not the tank, did some checks, mainly he emptied the tank from the bottom valve while turning off the water going in the tank, after filled up pressure came back to the hot water, he was satisfied it was not the tank and left and wished me luck. in the bathroom next to the tank i have the washer, a large bassin and behind the wall the 2 seat tub, if ever i draw hot water at a certain degree of pressure (3 quarters of the way) the cold water pipe knocks loudly a few times then the hot water stops, again in the whole household, but as soon as a few minutes later it is back fine. if i draw hot water from the 2 bathrooms and bath from the main floor it does not do it, either from the kitchen, just the washer, bassin and large bath. any ideas ? i check all the valves i could access in the house and they are fully open, everything works fine. I did several months ago loose some pressure on my tap in the kitchen, but i am blamming the hardware because when I remove it the pressure is ok. help ! I would love to avoid calling a plumber right now, money is a bit tight. thank you !