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Old 04-15-2012, 12:47 PM   #1
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Shower valve mixing hot and cold


Annoying situation in 2 story house recently moved in to, built in 1980, happening in 2 bathrooms: master and kids (both upstairs). I heat the water with an electric tankless heater.

Kids (knob pull and turn to control temp. Spigot at bottom to send water to showerhead/hose: Upon opening the hot water, it gets hot and nice. Very suddenly it changes to very cold and requires moving away. Then it returns to a tolerable semi-warmish. I replaced the Moen mixer cartridge just in case it was the culprit, but upon testing, the behavior continues. I clarify that no other device or shower is fighting for hot water with this shower; I was completely alone this morning when I changed the cartridge, and no dishwasher or clothes washer was on at the time. This is typically the case when the kids shower. I turned on the hot in the faucet/sink, and it was plenty hot.

Master (brand new redone shower and diverter valve that has normal showerhead and ceiling showerhead): the water comes out so hot, that I have to turn it down a bit. On occasion, a blast of cold water comes down, and have to jump from under the water. Slowly it returns to warm again.

I hope I have given as much information as needed. The heater is definitely adequate for the 4 of us showering, and we rarely use hot water to wash clothes.

Any suggestions to try out?
Thanks

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Old 04-15-2012, 04:05 PM   #2
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Shower valve mixing hot and cold


Sounds like the tankless water heater needs adjusting----it's not the mixer valves---it's the water heater---get a technicion to look at it---what brand --model is it?

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Old 04-15-2012, 04:19 PM   #3
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Shower valve mixing hot and cold


i will check brand of heater. what do you mean by adjust? i turned up the heat a bit, but how will that affect things?
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Old 04-15-2012, 04:23 PM   #4
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Shower valve mixing hot and cold


Those things have a little computer board and sensors--some have had the same issues you are describing---hot--then blast of cold--then just about right.

Usually means a call to the water heater tec.
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Old 04-15-2012, 05:42 PM   #5
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Shower valve mixing hot and cold


Sounds like the "Cold Water Sandwich", which is unfortunately normal if the elements have cooled off and the water in the line is still hot since the last person used it.

You get the nice instantly hot water that was still in the line from the last time the elements fired up first, then cold water rushes into the tankless and exits before the elements heat back up, then you get progressively warmer water as the elements kick back on.
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Old 04-15-2012, 07:30 PM   #6
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Shower valve mixing hot and cold


Does it happen only once, near the beginning of your shower?

If you don't use water for a few hours and then turn on the sink faucet, does it happen there exactly once if you wait long enough?
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Old 04-16-2012, 08:40 AM   #7
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Shower valve mixing hot and cold


Quote:
Originally Posted by AllanJ View Post
Does it happen only once, near the beginning of your shower?

If you don't use water for a few hours and then turn on the sink faucet, does it happen there exactly once if you wait long enough?
Usual behavior is as follows:
Kids shower---starts cold (as normal), takes a few minutes for hot water to reach up there, and hot water remains. Nice shower, shampoo, etc, and suddenly, a blast of cold that sometimes remains, and sometimes slowly dissapears and returns to warmish--most of the time, it stays on the colder side.

Master shower---starts cold as normal, warms up, reaches volcanic boil, I regulate it to my liking (warm), sudden blast of cold, warm eventually returns.

Typically these happen at different times and with both baths on at different times.

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