I have a contractor here to redo my guest bath, which is in-between my main water line/hot water heater (tank) and my master bath. The master bath is on the farthest side of the house away from the main water line, while the guest bath is more towards the middle of the house.

The contractor just finished installing the new tub and the plumbing that connects to the tub. He just began putting up drywall today in preparation to do tile work tomorrow. My master bath seems to be the only problem in my house, but I can't test the under construction guest bathroom because nothing is hooked up right now.

The problem is that the master bath sink never gets hot water, and the master shower only gets hot water if the master bath sink's hot water spigot is turned on. When I have both turned on, the hot water spigot of the sink stays cold. As soon as I turn the hot water spigot off in the sink, the shower turns back to cold. I can almost control the hot water in the shower with the hot water spigot in the sink.

I tried running all of my spigots inside and out, then turning them off again just to try something but it didn't help. I even did it a second time. Any suggestions on what to do? I asked the contractor working on the bathroom if I should call a plumber, but he says he wants to come check it out tomorrow morning. Is there a chance that once the rest of the water can run to the guest bath again that things will get back to normal? Thank you for any assistance.

  • Do you have a tankless water heater? If so, the flow rate might be so low with a water saving shower head that the tankless isn't "seeing" the flow and turning on. Again, if tankless, the fix would be a shower head that flowed more water...not politically or environmentally correct, but a possible solution. I'm getting to be less and less enthusiastic about tankless WH. Too many issues. Jan 15, 2021 at 15:08
  • If your contractor is doing the plumbing work, it should be up to him to get it right, whether he does it or sub-contracts it out. Just make sure he's got everything working correctly before making final payment! If he has to come rip out walls to make it right to get his money, he'll do it, so he'll probably want to fix things before he gets to that point.
    – FreeMan
    Jan 15, 2021 at 17:09
  • It sounds like a mixing valve in the guest bath is probably the issue I even believe you might find examples of this on this site.
    – Ed Beal
    Jan 15, 2021 at 17:27

1 Answer 1


The issue was the mixing valve like was suggested in the comments. The contractor luckily listened to me and replaced it before starting the tile work. He said that he, "didn't think that was needed," and also said, "I am not a plumber". Thank you for all your help in the comments.

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