Water heater problems?

Question

yes it is me again. I am the one who added the apartment onto my house and we are sharing the same water heater. Well we cannot get cold water on the apartment side. The house side is fine. If I turn off the hot water to both sides I can get cold water on the apartment side. They tired to fix it with a expansion tank that has not worked. We still are getting hot to temid water on the apartment side. Here are some pictures of the hook up and then the "fix" can you tell what is going on?

http://s268.photobucket.com/albums/jj4/mdjgirl7/Water%20heater/?action=view&current=PICT0135.jpg

http://s268.photobucket.com/albums/jj4/mdjgirl7/?action=view&current=PICT0146.jpg

Answer 1

Had a look at your pics here as well as the ones with an earlier question.  Everything in the pictures is fine.  You should in most cases have an expansion tank, so that is good, but I would not at all expect it to solve this problem.

As the tank heats water, there is a certain amount of pressure generated.  The pressure can cause you some problems, but the important part to this question is the volume.  The pressure can be enough to cause 1 - a "jolt" of water when you first turn on a faucet, 2 - leaks or failures due to high water pressure, and 3 - just a bit of hot water entering the cold water pipe.  The amount of hot water might be enough to cause warm water from the cold faucet for a second or two, but certainly not enough to get hot water.

Also noticed a couple of suggestions that your cold water supply to the apartment is to close to the water heater.  No logic to that at all.  Other than the minimal volume of hot water you may get due to thermal expansion, the hot water will stay in the tank without a pressure supply to push it out.  The water would have to enter the heater through the cold inlet, circulate in the heater, then exit back out through the inlet.  Can't happen.

That is really all I am sure of.  Two things that I can think of, may be one of these or may not.  Again, the problem is not in your pictures, so this is total speculation.

It looks like you have PEX tubing running to the apartment. PEX is usually run to manifold in a central location, then smaller tubing runs to each fixture.  Some manifolds combine hot and cold distribution in a single unit.  A defect in such a unit could cause the problems you describe.  I would not call this likely, just a remote possibility.

I think the more likely culprit is a defective or incorrectly installed recirculating pump.  A long run of pipe causes a long delay in getting hot water to the faucets.  You may have to run the water for a minute or so before it gets hot.  One solution is to install a pump that pumps water from the hot supply and recirulates it back to the water heater.  

It is better to run a separate return line back to the water heater, but it is common to simply pump the water back into the cold line.  The pumps usually have a thermostat built in that shuts them off once the hot supply reaches a reasonable temperature.  When everything is working well, this is fine as the amount of hot water that enters the cold line is minimal.

I wonder if perhaps you have one of these pumps installed and it is pumping continuously.  This is at least plausible.  The pump pushes hot water into the cold supply at a slightly higher pressure than the static pressure of the system, so if it was running continuously you would get the water from the recirc pump instead of from the supply.  When you turn off the hot water, there is nothing for it to pump so you would get cold water.

Have a look under the bathroom vanity or kitchen sink -- maybe both -- these are the common places to install the pump.

Answer 2

Is the apartment completed?  If there's a shower roughed in (but hasn't been trimmed) and you have capped nipples  sticking out, make sure that either the hot or the cold is turned off (preferably the hot - hopefully there's an integrated stop).  On some shower mixers you may have to install the cartridge to prevent crossover (hot water bleeding through the mixer & resulting in tepid water everywhere).

Answer 3

Water will take the path of least resistance. The hot water in the tank, due to its being heated, will be at a slightly higher pressure than the cold water. Given that the cold water line to the apartment is so close to the tank, the opening of a cold water valve in the apartment gives the hot water at that higher pressure a path to escape the tank, overcoming the pressure of the cold water intended for the apartment. You have a couple of options. Where the blue line to the apartment is teed from above the tank: relocate that tee to between the ball valve which shuts off the cold water to the tank, and the newly installed expansion tank. That expansion tank should be the first thing the hot water can back up into. If that's still not enough to do the trick, then install a check valve on the horizontal line between the expansion tank and the hot water tank. That should definitely prevent the backflow of hot water to your cold water side. Good luck.