Water Heaters - hot water goes backwards into toilets and showers

This sounds stupid but it is true. For some reason, hot water comes out of the cold water intake pipe on our hotr water heater. It finds its way to all toliets, showers, taps etc when everything is turned off. After a few seconds of running the cold water on any of them, cold water starts to flow like it should. But the initial slug of water is warm. And none of these leak!! What could possibly be causing this?

Hello and Welcome Baldy to the Do It Yourself Web Site.

First thing to note is how the water lines are connected to the top of the water heater. Cold inlet must be on the right side. The inlet will be marked on the top of the water heater (inlet). So will or most likely to be, the hot water side be marked as outlet.

Next thing is to allow the hot water to run in one of the sinks. Only the hot water must be running. Than with one hand on the inlet and one hand on the outlet sides of the lines going into and out of the water heaters tank, note if the cold is cold and the hot is hot.

Allow time to pass to be sure. Start this test b4 the water is turned on. Have another person turn the water on while you hold onto the pipes. Need it determine the temps of the pipes both before test starts and during.

If that test works, that aspect is completed. Lines at the tank are connected correctly. Cold on the right and hot on the left.

If hot water only comes out of the pipes into the toilets and not the sinks, than it is safe to assume only the toilets lines are connected incorrectly.

The idea is to isloate the problem first. Note what facilities are effected. Once that is known, the problem will be easier to diagnose.

If only the toilet(s) are effected, the piping lines are crossed to only those facilities. Problem than is to determine where in the piping system the problem lies. Most likely in the walls, attic, slab or under house in the crawl space, etc.

Since there is only one line leading into a toilet, the problem is likely a crossed line or an interconnected line, etc. May also have some malfunctioning valve and or device on the tank or in the piping system, depending upon how the piping system is plumbed, etc.

If the entire house is effected, lines likely crossed at the tank or all lines in the house could be crossed, etc.

Several possibilities many be possible and or exist. Seen many in my years of field services and diagnosing problems for high bill complaints and energy conservation investigations.

Many like or similar problems require the expertise of a plumber when the determined cause cannot be easily determined or is piping and or plumbing lines, etc. Not a licensed plumber myself but hope some of the above helps or provides some insight.

I don't doubt the problem exists either. Rare but does happen.

"My Two Cents."

You dont say just how the pipeing is set up here on the hot water tank. Some time you have to put a hot water trap like in the cold water line to stop this. Home depot and lowes have them .Its like check valves that go on the hot and the cold water line. You have to make sure you put the right one on the hot and cold water line. There also is a loop like that you can put on the cold water line that will stop this . It would be called a thermal trap.I think what you have is the hot water is migrating back up in the cold water line is all. It will do this if you dont have any set up to stop it.

My .02 cents That makes you got .04 cents


ED ;)

I recently discovered a bad mixing valve, where for some reason after running the faucet the hot water began to bleed back down into the cold inlet pipe under the sink. A few washers later problem solved.