Tankless water heater problems

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by srshaw, May 2, 2005.

  1. srshaw

    srshaw New Member

    Messages:
    1
    We had a tankless water heater (Takagi TM1) installed several months ago, and the plumber added a recirculating line to the farthest bathroom. We have been living with a couple of problems that I cannot seem to get to the plumber to address. The first is that when the heater shuts off and then restarts just seconds later, a 30 second "bubble" of cold water enters the hot water line after the hot water in the supply line is used. Since the heater is already hot and only takes 3 seconds to fire, this seems ridiculous. We checked to make sure that hot and cold are not cross-connected.

    The second problem is that there is very low pressure/volume through the hot water system. The heater is rated at 9.6 GPM with the capacity to bring 6 GPM to 115 F, but when more than one fixture is on simultaneously the temperature an volume changes in any line are dramatic. The max amount of water that seems to move through the hot water system is 3.6 GPM. The plumbing is all the same, with the exception of the recirc loop, typically 3/4" with 1/2" stubbed out to fixtures.

    Any thoughts/help?
  2. tankless nightmares

    they are all trouble, and are just a general pain..


    might I suggest that you try shutting of that recirulation line and see if this
    eliminates part or all of your first of many more problems.to come ....

    Honestly , I have never heard of putting a recirulation line on a tankless system....it usually comes with a pump to pump and recurculate the water back to a hot tank of standing water... so you have instant hot water at all fixtures...all the time
    -----------------------
    It possible that you could actually be really over working that unit if you actually have water pumping through those little coils 24 hours a day....

    a recirulation line that runs 24 hours a day literally overworks normal tank type water heaters and runs up your heating bil too....

    so its got to be harder on those coils in that unit.

    Now, please Correct me if I am wrong, but I dont believe they were made to go with a re-cirulation line...

    I assume he put in a pump for an active recirlation system??

    surely the guy put in a shut off valve to kill that line and unplug the pump ??

    Try that first, just kill that recirualtion line first and see what happens...
    -------------------------------------------------------------------------

    http://www.askthebuilder.com/451_Tankless_Water_Heaters_-_Some_Surprising_Facts.shtml


    also , do you have a water conditioner to keep that coil from LIMEING UP
    correct?? what hardness is the water in your area. That could also be teh problem with the pressure....

    good luck, cause
    you got tons of fun ahead of you.... :D
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,247
    Location:
    Cave Creek, Arizona
    Tankless

    I am not sure why your heater is turning off and then back on 30 seconds later, but if the flow is not enough to keep the burner running, and a small amount of water is flowing through it, that water is going to be cold and will create a "bubble of cold water" in the pipe. Tankless heaters typically have an "enormous" pressure/volume loss as the flow rate increases.
  4. PEW

    PEW DIY Senior Member

    Messages:
    487
    Why in the world would a plumber install a recirc pump on a tankless heater!!!??!! It would cause the heater to short cycle like you describe, and sure would not want your gas bill! They are just not compatible!

    Not only would I shut it down, but also would close the recirc loop completely.

    Personally, I would look for another plumber!!

    Paul
  5. srdenny

    srdenny Plumbing Contractor

    Messages:
    361
    Location:
    SF Peninsula
    1) TM-1's are made to be used with a recirc pump. The unit has a built in controller that you wire the pump to thru a relay. A timer on the recirc pump would also be a good idea.
    2) The lack of flow is due to the screen on the cold water inlet being partially clogged (not your plumber's fault).
    3) Noritz (a competitor of Takagi) says to eliminate that slug of hot water, you should add a small 8-10 gal storage tank to the loop.
    See page 47 of: http://www.noritzamerica.com/plumbingdocs/N-084M-DV_Owner_Guide_and_Installation_Manual.pdf
  6. sounds like more fun

    well, you are into that can of worms now fella.

    It looks like it anyway...

    Now to get the thing working right, they want you to install some sort of holding tank 10 gallon or so>>>??

    Hmmmmmmmmmmmm lets see, just another 40 gallons and you got a normal 50 gal heater> Ok, I will do that too.......sure right...



    People will literally walk through the fires of hell just to keep some new
    "hi Tech " device working properly..

    if you jump through that hoop and actually install a 10 gallon holding tank, you are nuts.


    ------------------------------------------------------------------------
    I am wondering how often do they say you should run vinegar through the
    coils to clean out the calcium and lime deposits???

    Its just another manitainance issue, nothing major, easy to do..
    have they mentioned that to you yet??
    ------------------------------------------------------------------------

    Take my advice, when your wife starts to give you "mean ugly looks" starting probably in the next few months with her first lukewarm or ice cold shower,

    consider just chucking the whole thing and cutting your losses.

    its nothing to be ashamed of,
    hell, 5 years ago I bought internet stock too.



    boy are you in for some fun... :p :p
    Last edited: May 5, 2005
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