Water lukewarm in one shower - hot every else

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New Member
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Portland, ME
One shower is generally only getting likewarm water. I say generally because sometimes it will nice and steamy warm but this is rare and completely unpredictable. The water at the adjacent sink gets plenty hot as does the shower and sink at a neighboring bath down the hall. It is not the anti scalding device. I also replaced the mixing valve cartridge, though the old one didn’t appear particularly gummed up. When the water is at its highest setting, the pressure is good and the same as at the coldest. It’s a single handle moen shower valve with the tub filling spot below and shower head above. The tub spout also only gets lukewarm water. Our hot water comes directly off the furnace - not an electric hot water heater.

We moved into this house 6 months ago - for the first 2 months the water temperature was great. We then had an episode of terrible water pressure which was resolved by us changing out the sediment filter (new to private water maintenance after always being on city water). I believe the hot water issues started then, but it wasn’t an immediate thing. I thought switching out the mixing valve would resolve a blockage caused by sediment getting through but like I said it made no difference. I also would have thought if there is a blockage in the actual line there would be pressure issues which there are not.

I’ve searched all the forums and watched all the YouTube vids. I can’t afford a plumber so desperate for any advice or troubleshooting ideas. I’m lucky in that we do have an alternative functional place to bathe, but that secondary shower is a tiny standup and I’d love to have the option of giving my toddler a proper bath again.


Retired Defense Industry Engineer xxx
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New England
Water takes the path of least resistance. It sounds like you have a cross-over somewhere. A single-handle faucet can on some designs allow a cross-over. It depends somewhat on what position the handle is left at. TO check if that's the issue, shut the cold off at any single-handle faucets when the shower is only lukewarm and see if it makes any difference.
Hey, wait a minute.

This is awkward, but...


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