Low hot water pressure

Discussion in 'Tankless Water Heater Forum' started by Catherine E Shook, Jun 14, 2018.

  1. Catherine E Shook

    Catherine E Shook Cathy

    Joined:
    Jun 6, 2018
    Location:
    Houston, Texas
    Howdy y'all,
    Switched to tankless (marey brand - gas and runs on batteries) just shy of two years ago. Pressure was fine in whole house - worked great. Then it sprung a leak and I disconnected it to get it repaired. I left the inlet and outlet setting there in the attic - I did replace the shutoff valve (after I found out it didn't shut off anything).
    So we had no water on the hot water side of anything, but we still had great cold water. So I connected the cold inlet straight to the hot line to get pressure back for the showers. That is when we noticed the pressure had dropped dramatically (valve is open all the way).
    New tankless came in hooked everything back up and still low pressure on the hot side of everything.

    Gas is fine, just water pressure is low. I can feel it going into the tank and it seems fine, but in the outlet pipe the pressure is low. Oh, I have 24" of brass flexible pipe coming and going into Pex from the tankless.

    What could be the problem?
    Thanks
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Are you saying that you got a large pressure drop even though the water heater was totally bypassed? Even from the tub faucet.
     
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  4. Catherine E Shook

    Catherine E Shook Cathy

    Joined:
    Jun 6, 2018
    Location:
    Houston, Texas
    Yes, it was like a quarter of the cold side.
    From what I understand about the manifold system (that distributes the water) it has two tanks one for cold and one for hot. So if a line a line if thinking us a line got blocked - then every hot line is blocked.
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Are you saying that the hot water output goes to a manifold? Tell us the make and model of the manifold, and/or post a photo of the manifold and the path to the manifold if close to the hot water heater.

    I would be thinking about a blockage near the input of the manifold. Maybe you could backflush that by disconnecting the input, connecting cold to hot at some place such as at the laundry connections, and pushing cold backwards through the manifold.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    WHen you replaced that valve, was the old one a full-port valve and the new one is a different type? Is the valve fully opened? If you haven't demineralized the tankless system, that could be part of the issue.
     
  7. Catherine E Shook

    Catherine E Shook Cathy

    Joined:
    Jun 6, 2018
    Location:
    Houston, Texas
    @Reach4 - Ugh, I hope that is not it - there is 6 inches of PEX pipe visible before the manifold. The manifold is in the garage and the tankless is in the Attic two stories up- so the water comes in to the garage goes up to the attic back down to the garage then out to each location. I haven't made it out to the garage to see what make it is.


    @jadnashua - the valve is different - original one was used in pex line I put this one at the end of pex line before the brass flex pipe, it is fully open. Tankless is new - instead of parts they replaced whole unit.
     
  8. Catherine E Shook

    Catherine E Shook Cathy

    Joined:
    Jun 6, 2018
    Location:
    Houston, Texas
    Well nothing in the lines, but it turns out there was another valve further up the line that got flipped half way when the PEX was moved.
     
    Reach4 likes this.
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