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Hot water

Discussion in 'Post Yacht' started by Kevin Lippe, Oct 8, 2017.

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  1. Kevin Lippe, Oct 8, 2017
    #1
    Kevin Lippe

    Kevin Lippe New Member

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    Maybe someone already asked this but here it is again . 1985 Post 43 . Every time the pool pump kicks on my hot water turns cold for about 5 seconds then turns hot again . It happens in all sinks and the shower so I know it's not just a mixing valve . Anyone have a suggestion for a cure ?
  2. rpontual, Oct 8, 2017
    #2
    rpontual

    rpontual Member

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    I do not know your boat, but my guess is that you have a check valve by the hot water tank. I suggest inspecting if the check valve is faulty.

    My theory is that when the pump comes on it raises the pressure on the cold side moving cold water to the hot water tank that might have a bit of air. Without the check valve and tap is open the water may move back in the tank through is outlet.
  3. Davidoc, Oct 8, 2017
    #3
    Davidoc

    Davidoc Senior Member

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    Boy that's a good one. I bet that makes you mad when you're taking a hot shower. What pressure are you running when the pump shuts off?
  4. truckman, Oct 9, 2017
    #4
    truckman

    truckman New Member

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    The problem is not the check valve. The water after the tank in the
    supply lines gets cold and until you run the hot for a few seconds to
    purge the line of the cooled water, its not going to be hot.
  5. praetorian47, Oct 9, 2017
    #5
    praetorian47

    praetorian47 Senior Member

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    I had a similar problem in the beginning of the year. My hot water would only last about 5 minutes. Eventually the problem went away and I can shower as long as I want without running out. Somebody mentioned I should get a check valve for the hot water as maybe there was some issue - but that wouldn't explain why it went away.
    On the galley sink, I get hot water no matter what often - especially after the engine has run. There is no hot water/engine interaction that should cause this. It only affects the galley sink, and that tap is brand new.

    I'm planning on redoing all the plumbing in the engine room anyway just to clean it up.
  6. Capt Ralph, Oct 9, 2017
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    I remember the transom shower valves were both left on and the out hose was shut off on our boat.
    The hot & Cold lines were tied together. Pending the pressure, pump off then warm, pump on then cool. Amazing how different temp water flows.
    Drove me crazy and I was convinced the water heater was messing up (dual elements). Then I noticed the transom valves were open. All fixed.

    Years later, our divers rinsed off with the transom shower water. That night, I recognized the symptom. Went out and turned the valves off.
    Luck for any body on the docks, no body was around.

    Would you have any shower, rinse system, lavatory that has a pass between the cold and hot water?
  7. mwwhit1, Oct 10, 2017
    #7
    mwwhit1

    mwwhit1 Senior Member

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    I have an 84 43. Have never experienced this. I'm thinking maybe you have a restriction in\out of the water heater? Therefore the cold side gets faster pressure and naturally pushes out more cold to the faucets until the pressure lowers again to let the hot flow. If you run full cold or full hot out of a faucet, are you seeing the same pressure fluctuations as the pool pump cycles? Does the pump cycle at the same interval\duration? If you end up seeing a difference where the hot is slower, try bypassing the hot water heater with a piece of hose (this is what I do when winterizing each year). If your pressure\interval\duration now act the same for hot\cold, probably build up inside the water heater that maybe you can run a solution through to dissolve?

    It's a start.
  8. Capt Ralph, Oct 10, 2017
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    If it's a SeaWard Alloy watet heater, oh heck yes this is a great idea.
  9. Bill106, Oct 10, 2017
    #9
    Bill106

    Bill106 Senior Member

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    I'm not sure of this particular boat but I've seen many installations with the hot water heater inlet feed tapped off the cold side as just another branch circuit, often only 1/2" ID. If you don't find any restrictions, adding a direct 3/4" feed from somewhere near the water pump's outlet might alleviate the momentary pressure differential.