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  1. #1
    Join Date
    Feb 2010
    Location
    Philadelphia
    Posts
    9

    Default Water Pressure Mystery

    I can't figure this one out. When I turn on my shower/tub (single lever pull system), the pressure starts out great. Then, after 20 seconds or so, the pressure reduces by half. No other faucets have this issue. So I have already replaced the shower cartridge (didn't help), cleaned the shower/tub diverter (didn't help), and replaced my shower head (again, didn't help). I recently had my hot water heater replaced, but the pressure was fine for months afterwards. I also have a natural gas boiler/radiator heating system, but no water is being drawn to it. If anyone has thoughts on other possible causes and solutions, I would be very thankful.

  2. #2
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,508

    Default Re: Water Pressure Mystery

    Does this matter what time of day?

    Are you on a well?

  3. #3
    Join Date
    Feb 2010
    Location
    Philadelphia
    Posts
    9

    Default Re: Water Pressure Mystery

    Thanks. I'm not on a well. My neighbors haven't experienced anything similar. Also, the time of day doesn't seem to affect the issue.

  4. #4
    Join Date
    Dec 2012
    Location
    New London County, CT
    Posts
    99

    Default Re: Water Pressure Mystery

    It could be the pressure balancing part of the shower valve. I don't think that is part of the cartridge. You could look at a parts diagram for that unit and see if it could be the problem.

  5. #5
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,508

    Default Re: Water Pressure Mystery

    Take the escutcheon plate from the valve assembly and snap a picture. A model number would be handy

  6. #6
    Join Date
    Feb 2010
    Location
    Philadelphia
    Posts
    9

    Default Re: Water Pressure Mystery

    Thanks, all. Last night, I checked on my hose fixtures to ensure that they hadn't frozen and punctured. While that wasn't the case, I noticed that the problem exists on these too. It seems as though the problem is easily seen on faucets that don't have aerators. Therefore, I think there is an issue with the main feed line. Thoughts?

  7. #7
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    5,438

    Default Re: Water Pressure Mystery

    Do you have a pressure reducing valve as your main water line enters the house?

  8. #8
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,418

    Default Re: Water Pressure Mystery

    Is there an expansion tank above your water heater? (There should be.) If so, this could be the explanation. There are a few possibilities that I can envision:
    • As water is heated, the expanding water backs up into the expansion tank. This results in an increase in pressure in the pipes (the water meter prevents the pressure from backflowing into the city main). When you open the faucet, you notice higher flow rate until the expansion tank is emptied.
    • When water is not flowing, the city water main builds up pressure in your pipes until it reaches what is known as the "static pressure." When you open the faucet, this static pressure is held until the expansion tank empties. A restriction in the incoming line (such as at the water meter, a pressure reducer, or corroded pipes & fittings) causes a reduction in water pressure.
    • You have a pressure regulator that is faulty and allows pressure to build up when water isn't flowing but is unable to maintain that pressure when water IS flowing.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  9. #9
    Join Date
    Feb 2010
    Location
    Philadelphia
    Posts
    9

    Default Re: Water Pressure Mystery

    Thanks, Fencepost. I do have the expansion tank above my water heater. Since I seem to experience the problem at hose faucets and in the shower with only cold water, I believe I might have a clogged supply line. Any thoughts on a good way to clear it?

  10. #10
    Join Date
    Jan 2008
    Posts
    1,330

    Default Re: Water Pressure Mystery

    The WH expansion tank should be on the cold (inlet) side, thus if it is assisting pressure temporarily it will exhibit the same effect on all cold water lines because that's what it is acting upon. It's put there because with the hot faucets closed, any expansion can only go the other way- back into the cold water inlet.

    It sounds like a pressure regulator issue to me. Look for a water pressure regulator by tracing a cold line back to where the cold water comes into the house- you may find it anywhere between that point and where the first pipe or fixture draws from, although they're usually located wherever the water line enters or very close to it. Also check at the meter box; a retrofitted regulator may have been located just downstream of the meter in more temperate climes where it won't freeze. Not common but I've seen it happen here a bit.

    Phil

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