Symptoms: When using shower, cold water soon (2 minutes) will supply warm or hot water. i.e without turning the hot valve on, and only turning cold valve on, the water out of showerhead gets warm or hot.

The shower has an American Standard single handle valve. I changed the cartridge but situation is the same. The old cartridge was missing one o-ring by the ceramic disk anyways.

This problem is only seen in one bath (with single handle), other baths don't have this issue. And none of the faucets in the kitchen or vanity sink have this issue. This bath is the closets one to the water heater unit.

It was suggested that I have a "cross over" problem, typically caused by single handle faucets. There are two such single handle faucets in the building. One upstairs vanity sink faucet and one right below it, ie the shower having this problem.

Isolate vanity sink: I closed off both cold and hot supply lines to the vanity sink faucet but the problem remains. While doing this test, I noticed that hot line supply to the vanity sink was turn all way on. I lowered that.

I checked the water heater and noticed that temp is set to "VERY HOT", touched the cold supply pipe and it was warm. I lowered that to "hot". Cold supply pipe is no longer warm to touch.

One more data point, there seems to be some temp fluctuations in all the showers. Water temp is adjusted, a few minutes later, suddenly the temp drops to very cold, requiring increase in hot supply, then it is too hot, requiring decrease in hot supply.

It was also suggested that the washer has a mix valve in it that could cause this sort of cross over.

Any ideas ?

4 Answers 4


I can think of two reasons that this would happen.

1) The balancing valve may be sticking.

2) There could be a bypass somewhere in your system. (Check this first). The way this happens is when there is a direct path between the hot water and the cold water, for example if you have a hose on your laundry tub with a shutoff on the hose. If you leave the faucet turned on, but the hose turned off, that creates a bypass. Faulty cartridges in a single handle faucet can also cause a bypass depending on they way they are made.


I've seen more of these things (single-handle shower valves) installed with the supply waterlines backwards than correctly, so that's going to be my answer. I don't know why that is, I just know that it is incredibly common for some reason.

You get hot on the cold setting. Do you get cold on the hot setting?

I doubt there is any advantage to having the vanity sink shutoff partially closed. The purpose of a shutoff valve is to shut the supply off at the fixture, nothing more.

  • I get hot from hot and get hot/warm from cold. Again, for the first couple of minutes, I get cold from cold, then having only cold running, the water gets warm.
    – Medi
    Nov 20, 2013 at 5:29
  • Do you have access to the waterlines so that you could feel back along the cold water line to see where it turns from cold to hot? ie, run cold water on the nearest fixture (pipe-wise nearest) that stays cold if needed to disambiguate cold from hot, then run this shower on cold and try to track the warm back along the cold supply. If the supply does not get warm, it's somehow internal to the valve - if the cold supply does get warm, it comes from somewhere. If the pipes are all buried in walls this is hard to do, if out in a basement or utility area it's easier.
    – Ecnerwal
    Nov 20, 2013 at 15:16
  • Unfortunately the pipes are buried in walls. I'll have to open the walls. I keep that in mind.
    – Medi
    Nov 21, 2013 at 7:27
  • 1
    At this point I would phone American Standard (800-488-8049) for technical support.
    – getterdun
    Nov 22, 2013 at 18:50
  • You can check various cold lines where they come out of the wall - so if you suspect the clothes washer, turn on this shower while touching the cold line for the clothes washer and see if it gets warm. Or just run around and feel all the cold lines at each fixture where they come out of the wall, then (running only this shower on "cold") go back around and see if one of them gets warm.
    – Ecnerwal
    Nov 22, 2013 at 19:18

From my experience, some single handle shower cartridges cause hot water crossover (bypass) due to mineral buildup on the pressure balance or scald prevention device inside of the cartridge. (often a stainless steel piston is involved in the pressure balance design, and when it gets fouled by minerals in the water, it affects the temperature control. ) I have only seen one case of a Washing machine causing the bypass, and that was largely due to a recirculation line and proximity to the water heater. Good luck.


We replaced the pressure tank and that seemed to help

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