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This question already has an answer here:

I saw a similar question asking why a shower gets hot/cold when toilet is flushed. My question is why does the person in the shower get cold If anyone anywhere in the house turns on the water? I cannot do dishes, run the washer or flush the toilet without someone getting froze out in the shower! Very frustrating!

marked as duplicate by Doresoom, Tester101 Jan 20 '15 at 12:12

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  • I forgot to add I have well water in this home. – Christina Marx Jan 15 '15 at 11:45
  • Not a duplicate. The question marked as duplicate asks why the shower gets cold OR HOT (though it only says cold in the title). Responses to the question marked as duplicate only answer why it gets hot. This question asks only why it gets cold. – dinosaur Mar 20 '17 at 17:37
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If flushing the toilet results in COLD water coming out of the shower it sounds like a pressure issue.

Typically flushing the toilet (which reduces the amount of cold water pressure in the line), would cause the shower to become too hot.

However, if the pressure in your system comes prior to where the cold feeds the hot water tank, then flushing the toilet could cause a pressure reduction in the hot line causing the hot line to diminish.

Solution would presumably be a pressure tank addition to the feed to the water heater before the tank but after the junction with the cold water, and a check valve to ensure the tank can only pressurize in one direction.

Suggest strongly you consult a plumber on this.

  • I am not sure this is true with the new anti-scalding valves. On the last 10-15 I have installed I have noticed exactly what the OP mentions, with any drop in pressure it goes cold. You are absolutely right on older valves though. – DMoore Jan 15 '15 at 16:33
  • Was there any mention of an anti-scalding valve in the OP? – The Evil Greebo Jan 16 '15 at 13:37
  • "flushing the toilet could cause a pressure reduction in the hot line causing the hot line to diminish" -- Wouldn't it also cause a pressure reduction in the cold line? Then hot and cold pressures would be reduced equally and the shower would stay the same temperature. Why would pressure in the hot line (and not the cold line) be reduced? – dinosaur Mar 20 '17 at 17:35
  • Did you miss the first sentence in my answer? – The Evil Greebo Mar 20 '17 at 19:40

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