We have a weird problem with hot water running cold in our apartment. At all of the faucets and taps we only get hot water for a minute or two and have to turn off the faucet/tap for 30 seconds and back on again to get hot water. Then the same thing happens again.

To get continuous hot water in any of the hot faucets downstairs, we have to leave the shower faucet upstairs running on hot. In the bathroom downstairs, to get continuous hot water out of the sink, we have to leave the shower faucet downstairs running on hot. Whilst this is happening, the water coming out of the shower faucet is freezing cold. As soon as you turn off the hot tap in the sink, the shower faucet water warms up again. Of course, until it cools down because of the original problem.

We had a plumber come in and he thinks it is a cross connection and that the check valve was in the wrong position and ought to be located on the cold pipe closer to the water heater.

Here is a photo of our plumbing configuration next to our water heater:


On the far left is a 1/2 inch pipe, what we think is a return line. Next to that is the hot water pipe and to the right, the other pipe going in to the water heater is the cold pipe.

Now, behind the flue we have a check valve with an arrow pointing to the right ->, which is connected to the cold water line.

One last thing. The return line and cold pipe are warm if we don't run water for a while, but today I ran the hot faucet for a couple of minutes in the shower and went down to the basement to check and both the return line and cold pipe were freezing cold.

So... I'm wondering if this configuration is correct or if indeed the check valve is in the wrong place, or might need replacing? Could it be the mixing valves in the shower faucets?

Any advice much appreciated. Thanks so much! I am getting desperate at this point.