Poor hot water pressure in shower

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by David Saperstein, Jun 13, 2021.

  1. David Saperstein

    David Saperstein New Member

    Joined:
    Jun 13, 2021
    Location:
    Seattle, WA
    I have a Grohe 34-122 shower mixing valve. I have cleaned the check valves and shower heads. The hot water pressure is good in the rest of the house (including the same bathroom sink) and the cold water pressure in the shower is great. The hot water in the shower is a dribble. I have cold water flushed the hot water pipes for 2 hrs, no help. My next thought was to replace the check valve on the mixing valve. Is this a possible source of the problem? I have had sediment in the lines, but have a filter system now. I am thinking if it is not in the valve it must be the pipes near the shower.
    Should I replace the cartridge too? If these things fail, is there anyway to unclog pipes without ripping out tile and walls?
    Thanks

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    Last edited by a moderator: Jun 13, 2021
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Clean any screens. THen, do a volume check. People equate volume to pressure...but in reality, the pressure is likely fine, but there is a restriction, limiting the volume available. If you were to cap the outlet, then turn the water on, the pressure would be the same. A shower head only works well when there is more volume available than the head can pass...this causes the water to back up behind the restriction, and speed up through it, trying to keep the volume/time the same. No restriction in the head (not enough volume), no acceleration through the head so it acts like a rain shower versus a nozzle.

    If sediment got into the cartridges, then you may have to replace them as well.
     
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  4. David Saperstein

    David Saperstein New Member

    Joined:
    Jun 13, 2021
    Location:
    Seattle, WA
    Thanks for the reply. I do need some clarification. How do I do a volume check? I have cleaned all the screens. Previously, this was the issue. I cleaned the screens a few years ago and the pressure was pretty good afterwards. This time when I took the screens off, they were clean. This shower has 2 separate shower heads and both suffer from the seam low pressure/volume issue. It is really just a dribble coming out now. When I take the heads off, same thing just a dribble. When I did a cold water flush (blocked the flow in shower head, turned off the water to my water heater (instant on gas type) and opened the hot water valve in the other bathroom tub and turned on the cold water full in the affected shower) there was only a dribble coming out in the bath tub. No significant debris. I flushed for 2 hours. No change in flow. All of the other hot water spigots in the house work fine (3 sinks, bath tub).

    Hate to be repetitive, but do these check valves fail in a way that could prevent flow? I have ordered a new one to see. I will also replace he cartridge, but if there were sediment in the cartridge, would it only effect the hot water? Again, the cold water flow in this shower is fine.
    Thanks
     
  5. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    Is there an additional stop valves for the hot and cold such as in the basement or crawl space? If yes suspect that the washer for the hot stop valve may have caplased or came off the stem and it's just jamming up the works.

    At the shower body close the cold and hot stop valves (part #5). Remove the cartridge. Open the hot stop valve slowly and water will come out the cartridge body area. You may need a pail and a few towels since the water may spray all over the place. You might want to place sock over it so as to catch any debris. Or place your hand with a rag and allow the water to flow out of the tub spot or shower head. Keep opening the hot stop valve until you think it is clear. If it dribbles then the block is before the valve body since the screen is clear.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    The simple way on a volume check is just a bucket and a clock.

    A typical showerhead by US regulation cannot pass more than 2.5gpm, and most will be lower than that. There's no flow maximum on a tub outlet, but you're limited by the supply pipes and the valve...most tub spouts don't limit the flow, so typical is in teh 5gpm range.

    Another test would be to remove the shower head and then measure how much volume you get out of the shower arm in gpm. If you have really hard water, the water jets of the head may be partially closed off by mineral deposits. That actually would tend to make the velocity higher, but keep the volume way down. If so, the easier thing is to replace the head, but you could try letting it soak in a bowl of vinegar or LimeAway over night.
     
    Last edited: Jun 17, 2021
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