Hot water pressure/flow at spout fades as it gets warm

Discussion in 'Shower & Bathtub Forum & Blog' started by Rick Clancy, May 31, 2021.

  1. Rick Clancy

    Rick Clancy New Member

    Joined:
    May 31, 2021
    Location:
    02152
    Hi. First time post-er here from Winthrop MA.
    What could be the cause of my hot water pressure (flow) dropping as it become warmer. This happens only in one bathroom. I turn on the hot water and the pressure/flow is fine until the hot water makes it to the fixture then the hot water pressure/flow drops almost to a trickle and I have to open up the hot valve further for more flow.
    It's in an old 2 family house - 2nd floor unit.
    Neither the shower or sink have mixers - The shower/tub is old school with 4 Cross handles (separate hot and cold for tub and shower). I think valves are Eljer from about 1940s - maybe 15 years ago I brought the leaking shower hot valve to supply hose (Republic in Watertown MA) and was told that I could not buy (no longer made) a stand alone hot valve so I bought a cold which turns opposite and has worked well for many years. Obviously this would not affect the sink.
    The cold water is fine and this only happens to hot -shower and sink. It doesn't seem to happen in the kitchen or other 1/2 bath, but they have low flow and don't know if that would mask it happening there.
    Anyone have any thoughts? Thank you!!
     
  2. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    As materials heat up, they expand. With the age of the faucet, it's likely it utilizes separate stem and bonnet assembly controls with a faucet washer on the end of each stem. The flow rate will be controlled by adjusting the space between the stem washer and a brass mating seat inside the faucet. As the soft washer expands from the hot water flowing past, then the space between the washer and seat will be reduced, thereby reducing the flow rate.

    It's also possible the brass seat has loosened within the faucet. The seat is commonly threaded and tightened into the faucet using a hex shaped Allen wrench.

    Another possibility is the stem assembly is worn, which is then allowing excessive play between the faucet stem and the bonnet assembly the stem is threaded into. Wear is usually checked by turning on the faucet a small amount, and then gently pushing inward on the faucet handle to detect the amount of stem movement and the amount of flow change compared to when pulling the handle straight outward.

    Suggest removing the stem and bonnet assembly so determine if a matching replacement continues to be available from a plumbing supplier local to your area. If the complete assembly is not available, perhaps replacing the soft washers, O rings etc and retightening the brass seat will be sufficient yo reduce the flow variance.
     
    Last edited: May 31, 2021
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  4. Rick Clancy

    Rick Clancy New Member

    Joined:
    May 31, 2021
    Location:
    02152
    @Bannerman
    Many thanks for your reply. Unfortunately, when I checked 15 years ago the Hot stems were no longer available due to code requirement for anti-scald valves. But the cold was available. So I installed the cold stem in the hot and ,while it turns opposite, it worked fine. I did replace the end washer a year ago to correct a drip... I got the same size washer but would substituting a thinner washer alleviate the fading hot problem a bit since it wouldn't expand as much?
    I'm hesitant to do away with the separate controls and refit the shower with a balance anti-scald control because I LOVE the full water flow ...I have removed the low-flow insert from the head and I don't know if a single handle balancer has such restrictive parts and would not want to risk loosing my (at least) 5 gallon per minute flow :) In your experience do the anti scald valves typically restrict flow or is that just the job of the shower head?
    Thanks for the advice!! I'll replace all the rings and washers. But it's interesting that it happens on but the shower and the sink. Maybe a coincidence... but I wonder - is there anything at the water heater that I should check out?
    Rick
     
  5. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    In some faucet brands, the stem washer for the hot side is a different material than for the cold side. I have seen some faucets use a harder Red colour washer for hot, and the more common softer Black washer for cold so you may want to check if an alternate washer is available. You will be unlikely to find alternate washers at HD, Lowes etc so you may need to contact a speciality plumbing supply that normally supports the plumbing trade.

    You said the water is hot and there are no issues with flow to other faucets. Since opening the problem faucets further alleviates the issue, the problem appears to be the two faucets you mention, not the WH.
     
  6. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    discussion only -- not actionable:

    Back in the old days, people used the red fiber washers for hot stems. I don't know if they had a more favorable coefficient of expansion, or if they were just more long-lived with hot than natural rubber. Newer compounds should withstand hot quite nicely.

    It seems to me that a washer with a desirable coefficient of expansion could in theory be designed, because rubber has a negative coefficient of expansion, and most things are positive. But since most faucets have switched to cartridges, I don't see a good market.

    https://en.wikipedia.org/wiki/Talk:Thermal_expansion#Rubber_has_Negative_TE. discusses if that is true about rubber, but in any case, there are materials with negative
     
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