Recently I installed a second hot water at the MBR and kitchen end of my long rancher. (Formerly, it took a LONG time for HW to reach the Master Bath and Kitchen; the new HW heater remedied that.) Howe ver, now when the shower is in use and someone runs hot or cold water in the kitchen or Master Bath sink, the water termperature in the shower changes drastically. Before I installed the new HW heater this occurred only very slightly. Now it is quite pronounced, making for a very uncomfortable shower (usually accompanied by a scream.) I've checked all the valves and they are all wide open. Any suggestions?

Some dirt may have got into the lines and they aren't fully open or one of the gate valves seems open but may not be. Even though you checked them.
Were there any faucets changed also?
How old was the other HWH?


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Some dirt may have got into the lines and they arent fully open or one of the gate valves seems open but may not be. Even though you checked them.
Were there any faucets changed also?
How old ws the other HWH?


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Hmmmm. Thanks. Good questions. I'm pretty sure no dirt got into the work, but it's possible. The shower faucet and those in the master bath are all new, installed at the same time as the HWH. The old HWH at the other end of the house is about 10 years old, I believe. It sounds like you're thinking that there's a blockage. Hmmmmm. Could it be a problem with the "anti-scold" feature of the new shower faucet control?

A couple of other things may be going here also. Where does the water service line come into first.
The new HWH, how was that tied in and what size pipe for supply and the vertical riser pipe form that heater and the set up on the other one ?

The old heater, I would check the old HWH Nipples ports to see if that's restricted. One HWH may rob the other not being more in equal pressure and balance.
You can also create a different venture effect on two pressure changes and the one side of the line loses enough pressure to the shpwer or vice a versa.

Clean Aerators on fixtures.

It sounds like the old days when there was 3/8 hot water lines and 1/2 cold lines and when someone flushes the toilet while person is the shower its Ouch to hot or cold when the hot is used in a another faucet and the shower is cold all of a sudden

I feel that could be the situation here and the tie in and the pressure changes.
Very detailed info on the tie in and size pipe and riser on new HWH and old HWH.

If its on a same line opposite from each other and the old heater is restricted in the nipples then when a faucet is putting demand on that in between line it pulls from the less restricted heater and that now robs hot from what it was supposed to feed and fights direction and takes the path of least resistance. If the old heater is restricted its just like the old 3/8 hot supply and that will always make a big change

So hears some more possibilities.

Aerators for dirt
Shower head restrictor dirt
Check old heater nipples to be clean and fully open to supply even pressure on the different demands.

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