We have a 30 cubic metre water tank that has a stopcock at the base in the pipe that goes underground. When the stopcock is turned off, an apparently endless amount of water still comes out of the taps in the building that is supplied. Perhaps the stopcock is not working, but it's hard to dismantle it without draining the tank. The outlet pipe is in the middle of the tank under 3 metres of water at the moment. I could try to use a long stick to put a plug over the pipe, but it isn't going to be easy through a tiny hole in the roof of the tank.
With the stopcock "off", after running a tap for a few minutes, the water gets decidedly warm. This is quite likely to be backflow from the solar-heated hot water cylinder on the roof. Except that there is a non-returrn valve inside the wall to prevent backflow. Perhaps that non-return valve has failed, in which case it means taking the wall apart to get at it.
Having possibly drained most of the hot water tank, when I turn the stopcock "on" again, I can't hear or feel any water flow through the stopcock.
Any guesses what is wrong? The stopcock or the non-return valve? Or both, or something else? I need to know in 12 hours :)