Hot water coming through cold water line

[ballvalve]

I think your hot water is just working its way up the pipes when at rest - see the links.

http://www.siouxchief.com/Supply/Fit...rap-Loop.M7LUX

http://www.waterheaterrescue.com/pag...ap-issues.html

http://www.energysavers.gov/your_hom.../mytopic=13100

[mrdojo]

Well, I finally got this all resolved so I thought I'd come back and report. First off for Hackney plumbing: I never did try exactly what you had mentioned so I can't say what the result of that was. To ballvalve: regarding your comment: "When you open a hot tap, the cold water cannot flow in the opposite direction. I dont care where your bag in a can is located." You're right, and this was my "fix" for getting cold water more quickly - turn on a hot water tap at another location, then turn on the cold where I was getting a drink. Since the hot water can't flow both ways that seemed to do the trick.

But more to the point, this morning the original plumber finally came back and took off the expansion tank from the hot side and put a new smaller one on the cold side. This seems to have fixed it as was expected. Yea!! He said he had never seen that happen, but was nice enough about it. I just wish he wouldn't have been so hard to track down and get out to fix it. But, all's well that ends well I suppose.

[jadnashua]

All of the installation instructions for an expansion tank call for it to be on the cold side...the ones designed for potable water are NOT designed for use on hot, plus, some of the other issues you noted. On the cold side, any that might discharge would be cold, not creating any problems, and being cold, the bladder should last a much longer time as it was designed for.

They do make expansion tanks for boilers that go on the hot side (obviously!), but they are specifically NOT designed for potable water.

But, when setup properly, you rarely should get much more than a cup or so of water pushed into the expansion tank during a reheat situation. It sounds like the static pressure in the tank was low for your local water pressure, allowing much more hot water into the tank, making the problem worse, and stressing the expansion tank as well.