Hot Water Pressure Problems - One Faucet Only

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I've got a hot water pressure problem but only at one fixture: the 2 handle non-low flow fixture at my basement utility sink. It's your basic home-center utility sink fixture, the kind you can attach a garden hose to.
When I first turn on the hot water faucet I get a lot of pressure but as the water heats up, the pressure drops significantly, probably by half within 20 seconds.
I don't experience any pressure drop at any other fixture, not at the single handle sinks or showers fixtures nor at the two-handle fixture in a 2nd floor bathroom.
It's only at the utility sink where I experience this problem. BTW it's nothing new, I don't even recall when it first started...it's been years. I'm just finally getting around to asking about it.
Any ideas? Could it be that all of the other fixtures are low flow so that they never allow as much water to flow so that the drop in pressure is never noticed since they are maxed out at all times anyway?
Thanks.
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and I figure it is just a thermal thing.
R
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Yes, I have to open the faucet much farther than the cold to get enough hot water to make the water warm.
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I've seen other faucets do that too. My guess would be that the washer in the faucet expands with the temp increase, causing the flow to decrease.
As long as you can get a high flow rate with the faucet wide open, you can pretty much rule out kinked pipes somewhere, obstructions, etc. I'd try changing the washer and see what happens.
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wrote:

I know that everyone is trying to help, but I've already posted a couple of times that the stems, washers and seats were already changed.
The problem existed before the rebuild and remains afterwards.
I guess it's possible that the washer expansion problem "followed" the stem change i.e. faulty washers before and after. If that's the case, I guess I should buy washers from a different store and hope that they use a different brand/manufacturer.
I guess it's worth a try.
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On Sun, 19 Feb 2012 17:50:45 +0000 (UTC), DerbyDad03

What kind of piping? You didn't mention the cold water side of the faucet. Does the pressure drop when that's opened?
--Vic
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wrote:

1/2" copper.
The problem is only on the hot side at this one fixture.
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On Sun, 19 Feb 2012 18:01:39 +0000 (UTC), DerbyDad03

If it bothered me, I'd pull the stem and see if there's debris/sediment in there.
--Vic
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wrote:

Already been done.
I had a worn washer and seat on the cold side, so I replaced the entire stems on both sides a few months ago.
The problem was there before that and it's still there now. Replacing the stems had no effect.
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On Sun, 19 Feb 2012 18:24:03 +0000 (UTC), DerbyDad03

Then what's left is an obstruction in the hot water piping before the faucet. Your hot water and cold water pressure should be the same, except for a minor bit more on hot water when first opened due to expansion. And that's insignificant. Since the other faucets are low flow, they might have the same issue, but it's not noticeable, Depends on how the piping is branched and sized, but "normally" the basement has slightly more pressure than upper floors due to head pressure. Barring sizing and branching, the only other place to look is the inlet valve to the HW tank, or other valves unique to the hot water side.
--Vic
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On 2/19/2012 12:49 PM, Vic Smith wrote: ...

You've asked indirectly, I was going to ask if by chance the hot water side at this fixture is plumbed small for some reason.
What about the cutoff valve at the fixture--restriction there by any chance?
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All plumbing in the house is 1/2" copper. There's no down-sizing to this fixture.
The shutoff for hot side of this faucet is a fully open ball valve.
How would a restriction in the plumbing to that side of the fixture cause 20 seconds of high flow and then a descreasing amount as the water gets hot?
Wouldn't the restriction be there at all times, always restricting the flow?
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On 2/19/2012 2:18 PM, DerbyDad03 wrote: ...

If it were a loose impediment, not necessarily...
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On 2/19/2012 2:34 PM, dpb wrote:

OBTW, you can eliminate/confirm the idea of the other faucets by removing the aerator from one and testing. If it's flow-limiting so don't notice the symptom, removing the restrictor will uncover that...
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And impediment that expands when it gets hot.
Christopher A. Young Learn more about Jesus www.lds.org .
On 2/19/2012 2:18 PM, DerbyDad03 wrote: ...

If it were a loose impediment, not necessarily...
--



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On Sun, 19 Feb 2012 20:18:08 +0000 (UTC), DerbyDad03

There's pressure, and flow (volume.) When the faucet is off, all water in the piping gets pressurized. But once the pressure has reduced by ejecting water from the faucet, it takes sufficient flow to maintain the pressure
The timing doesn't seem right for that from what you said - 20 seconds? But if you have an expansion tank, it may take that long to depressurize. Then the flow restriction shows itself. Since you have copper, a valve is the most likely suspect. Another WAG is the HW tank is scaled up enough to restrict flow. If you've pulled all the associated valve stems and verified the valves are unrestricted, the only thing left is to take apart the lines before and after the tank to pin it down. I think you'll live with it as it is, but maybe I'm wrong.
--Vic
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wrote:

Well, I dont have an expansion tank, so we can eliminate that as part of the situation.
As far as eliminating the ball valve shut off as a possible cause, that could easily be done with a couple of Sharkbites and some Pex as a bypass.
In fact, I could flush the line by the tapping in before the shutoff and letting the Pex hang in the sink as I turn the main back on. Then I could tap in before the faucet (creating the bypass) then let the system pressurize and open the faucet to see what happens.
Im not sure what you mean by "take apart the lines before and after the tank to pin it down."
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On Sun, 19 Feb 2012 21:48:29 +0000 (UTC), DerbyDad03

Your bypass idea is breaking into (I used "take apart".) the line after the tank. If you have the same flow problem, the next step would be to check flow going into the tank, If that's good it's the tank restricting the flow. Don't know how your valves are set up. My tanks have always had a valve only on the outlet side. But some have both. Also have no stop valves on my laundry tub. And I never worked with copper, just galvanized. Sounds like you know the process.
--Vic
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Might be problems with a shut off faucet, upstream?
Christopher A. Young Learn more about Jesus www.lds.org .
Already been done.
I had a worn washer and seat on the cold side, so I replaced the entire stems on both sides a few months ago.
The problem was there before that and it's still there now. Replacing the stems had no effect.
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Sounds like a faucet washer expanding when heated, or maybe loose and needs to be tightned down. I'd think to replace both faucet washers while you have the water off.
Christopher A. Young Learn more about Jesus www.lds.org .
1/2" copper.
The problem is only on the hot side at this one fixture.
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