Why, when i turn on the hot water, does the water pressure slow down just when the water gets warm?
August 2, 2011 8:26 AM Subscribe
Why, when i turn on the hot water, does the water pressure slow down just when the water gets warm? I don't believe its a pressure reducer on the hot water tank, nor a special valve at the tap. i've seen this in literally 100 year old houses, brand new installs, hotels etc etc. Question came up because we are moving to a home with a tankless hot water heater and are curious if the same effect exists there...
Response by poster: let me restate it:
1. turn on hot water.
2. it comes out COLD and at a normal "fast" flow rate
3. as it warms up it progressively slows down (the flow rate)
4. once its hot its basically a trickle and needs to be turned up again
5. dear god why?
that's the question i'm after.
posted by chasles at 9:20 AM on August 2, 2011
1. turn on hot water.
2. it comes out COLD and at a normal "fast" flow rate
3. as it warms up it progressively slows down (the flow rate)
4. once its hot its basically a trickle and needs to be turned up again
5. dear god why?
that's the question i'm after.
posted by chasles at 9:20 AM on August 2, 2011
Best answer: Washers, valve parts, and other such things in the pluming expand as they heat up. When they expand, the fit changes, reducing flow.
posted by penguinicity at 9:23 AM on August 2, 2011 [1 favorite]
posted by penguinicity at 9:23 AM on August 2, 2011 [1 favorite]
Best answer: The gaskets in the faucet swell as they get warm. This reduces the flow of water.
posted by Chocolate Pickle at 10:25 AM on August 2, 2011 [1 favorite]
posted by Chocolate Pickle at 10:25 AM on August 2, 2011 [1 favorite]
As for whether it will happen with your tankless hot water system: maybe. The one in my current flat, amazingly, shows no loss of pressure whatsoever when the heat kicks in. It's perfect. But I've also had the opposite experience: a tankless system where the water slowed to such a trickle that the heater would turn off again(!) if you weren't quick enough to turn the tap on a bit further. (That flat nearly put me off tankless systems for good. If you turned the tap on too far once the water had become a hot trickle, the heater would fail to keep up and you'd get water barely above cold. Filling the flat's tiny, shallow, half-size bath took half an hour, and you had to watch the tap like a hawk throughout to make sure the flow stayed in the "hot" zone. Thank goodness there wasn't a shower.)
posted by ManyLeggedCreature at 10:28 AM on August 2, 2011
posted by ManyLeggedCreature at 10:28 AM on August 2, 2011
This happens now in my house, which has a heater tank. It didn't used to, but this started after I replaced some gaskets and washers that were leaking. So I assume it has something to do with the new gaskets swelling as they warm up, like CP said. (I sure hope a gap isn't opening up as things expand, and water isn't finding another path out of the pipes, like behind my walls!)
posted by Quietgal at 10:51 AM on August 2, 2011
posted by Quietgal at 10:51 AM on August 2, 2011
This thread is closed to new comments.
Every 6 months or so, my husband does something to the faucet in our bathtub, and it cleans a bunch of gunk out, then the hot water flows like crazy. Galvanized pipes can also have build-up all through the pipes so you'd have to re-plumb to fix that problem.
posted by peep at 8:35 AM on August 2, 2011