Hot Water Heater - hot water expanding back into cold pipes

[uncoolcentral]

When I run cold water at any faucet, the water gets hot after a few seconds, then gets cold again. I checked for crossed/touching pipes, and heating/defrost devices. None found.

So I figure that as the hot water heats in the hot water heater tank, it expands, sending hot water back up into the cold water intake line.

I understand that I can put a valve (bleeder or balloon, etc.) inline in the cold water intake line to prevent this backflow.

Is that correct?

If so, what is the valve called? Can you show an online example of availability? Are there any installation/operational concerns?

Or is there a different solution?

Thanks,

-Dan

[jadnashua]

They're called heat traps. They come in pairs, one for input one for output - they are also color coded to help you figure out which is which. They've got a sphere that floats or falls in the appropriate direction to seal the convection path, but opens when you turn on a faucet. One downside, because the hot water is more effectively held in the tank, it may take longer to get it when you want.

[uncoolcentral]

Interesting, but not what I was mentioning. How do these traps prevent/address pressure from building up in the tank? If hot water doesn't have anywhere to go, (no open faucets, can't go back into the cold send) pressure can get more than silly.

That's not to say that I know where the hot water would go with one of these (balloon or bleeder or whatever) valves I'm talking about installed.

Ideas?

[jadnashua]

I think that you'll find that it is convection...water does expand when it is heated, but not enough to push it up to the cold water faucet - if it did that, it would more likely push back out to the street rather than up to a closed end (otherwise the pipe or washer, or something would split, to relieve the pressure). Water doesn't compress - something has to give as it expands.

People run into problems if they have a pressure reduction valve (which acts as a one-way valve) sometimes. In that instance, an expansion tank is usually recommended/required to prevent blowing out a seal or pipe.

[hj]

If your analysis is correct, and that is not a given, then a check valve on the incoming water supply to the water heater, in conjunction with an expansion tank to minimize pressure build up, will cure it. But first I would do some checking to be sure that is actually the problem. It would normally only apply if the water heater was in a basement, and then you could feel the main cold water supply by the water heater to see if it was actually getting hot.

[uncoolcentral]

Right on. I'll confirm and reply back. Thanks