About 2 weeks ago our hot water started getting less and less hot, now it is completely cold. If I turn the cold angle stop off at the sink, so only the hot water line can feed the faucet, and turn it on, water flows. If I turn it to the completely hot setting water flows, but if I turn it to the completely cold setting the water stops. (No crossover in the faucet). Here is the tricky part, if I turn off the cold water feed to the hot water heater, with the faucet on hot only, the water will still run. This happens in all of my sinks except one. In the hookup closest to the hot water heater, if I hook the hose to the hot water angle valve and turn it on, HOT water flows out. If I then turn off the supply to the hot water heater, the flow stops (as it should). Only this one sink functions this way. When this is happening I can hear the water being taken out of the hot water heater, and new water being put in. When I turn on any other faucet it is not even trying to draw water out of the hot water heater, even if I have the cold angle valve on the faucet turned off (so it can only draw from the hot circuit). Also, I turned off the angle valves to the dishwasher and washer/dryer for all the tests.
To summarize, the faucet closest to the hot water heater works flawlessly. All other faucets will only run cold. When the cold water angle valve is turned off, and the faucet is turned onto hot, water runs, but is cold, and is not even trying to draw from the hot water heater. Everything seemed to work fine 2 weeks ago, and no plumbing has been tampered with.