Low water pressure in one shower and tub

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dipper, Jul 14, 2010.

  1. dipper

    dipper New Member

    Jul 14, 2010
    I recently moved into a 2-story house built in 1994. One shower and tub in a bathroom upstaires has very weak water flow (same for cold and hot water). The fauset over sink in the same bath has good flow/pressure.

    It is the one knob just turn system (positemp?). I removed the knob, disc, and catridge. And after I turned the water to the house back on, the water flow at the valve is weak. I studied the hole and did not find any stop like the one explained in http://www.youtube.com/watch?v=jnPNR6douzg&feature=related

    I also tried a new catridge and it didn't improve the water flow.

    There are two things that I can think of

    - could the pipe be clogged? The water heater that serve the bathroom was recently replaced. But I don't know if the shower/tub water flow was good before that.

    - could it be some stopsf/shut off somewhere nearby? how can I find out?

    Any suggestion/comments? Thanks!

    A puzzled mom:confused::(
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Do you get rust stained water out of this tub/shower valve? If so, they may have used iron nipples or fittings somewhere in the installation, and those are now filling up with rust. If the flow is poor through the valve body with the cartridge out, you've got a supply problem, not the valve. You may have to make a hole from the back to see what's going on. If that isn't a possibility, you may have to tear up the finshed wall in the shower. It's possible that crud dislodged when the water was off could have clogged the cartridge, but it should not be a problem with the new one. Remove the cartridge, then turn the water back on. Flush it out. It will spray everywhere, but should go into the tub instead of in the wall. If you can't get good flow there, you'll have to tear more apart to find the restriction.

    Some valves have filter screens burried in them. Those could be clogged. Your tub spout won't , but your showerhead might as well. If those are clogged, it can decrease the flow considerably.
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  4. dipper

    dipper New Member

    Jul 14, 2010
    Thank you for the answer, jadnashua.

    The water is clear out of tub/shower valve. I will flush the system first to see if it improves and give an update.

    I really do not want to tear up the wall :( But I am planning to live in this house for quite a while and this is my daughter's bathroom.
  5. sheila_zhou

    sheila_zhou New Member

    Aug 3, 2010
    Austin, TX
    I would like to give an update on this in case somebody experiences the same problem.

    The problem was fixed with a very low cost.

    After some study, we think the water supply should give better water flow at shower head than we got. So we believe there is something wrong after the catridge. Since the problem is for both tub and shower, our guess is the mixed chamber before the pipes splits. We spent sometime to using any tools we can find to clean the mixing chamber but all failed. Eventually, we put the catridge back and left tub faucet and shower head unattached. Then we blocked the tub pipe and fill the pipe including mix chamber with white vineger via the shower arm. We left it soaked over night - 10 hours. Then next morning, we removed the tub pipe plug. The water came out was light green. We didn't see any pieces of debris. The water flow at the shoer head about doubled and is suitable for a shower now.
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