Water Going Cold with Takagi Tankless

Discussion in 'Tankless Water Heater Forum' started by monty, Jan 27, 2010.

  1. monty

    monty Member

    May 1, 2006
    San Francisco
    Quick Follow Up:

    After contacting Takagi and getting the problem to occur with the cover off, with a good flow of water going through the heater, and no error codes - the Tech told me I needed to remove the flow sensor and soak it in CLR for a couple of hours - I haven't yet been able to do that but hope to soon.

    A new repalcement Flow Sensor is only $28 so if I still have problems I will buy a new one...
  2. monty

    monty Member

    May 1, 2006
    San Francisco
    Reporting back:

    I was finally able to soak the flow sensor in CLR for a few hours. With this back in place a new problem surfaced - I finally started to get an error code (4 LED blinks)

    I worked with Takagi Technical Support on the phone and completely cleaned the burners, heat exchanger, fan, pressure switch, and exhaust piping. There was a very small amount of dust on most items which I cleaned with an air compressor. I also cleaned/sanded the igniter and flame detector, and reassembled the unit. So far it is working great, and I am keeping my fingers crossed.

    Thanks again to everyone here for their help - I now am far too much of an expert on Takagi tankless heaters!
    Last edited: May 28, 2010
  3. Dave Lynch

    Dave Lynch New Member

    Apr 19, 2017
    Lancaster, PA
    I have been having shuttoff problems with my TKjr since I got it.

    I tried most of the suguestions here and elsewhere and finally came up with something that is working and telling me what the problem is.
    First the symptoms:

    The water suddenly turns cold. This is frequent and I beleive more common in winter.
    Once it shifts to cold I can not get hot back until I turn the faucet (or shower) off for a minute or so and back on.
    I do NOT need to "reset" the tkjr.
    The problem gets less frequent the longer the water is running.
    i.e. when it is bad I usually have to "cycle" the shower four or five times before the water will remain hot for 5-10 minutes.

    The problem occurs with most uses that involve mixing hot and cold water (should have been a BIG clue).
    But is most common with the shower.

    I have tried making sure there was no obstruction to venting.
    Running a separate tap with straight hot to increase the demand for hot,
    Many of the rest of the suggestions here.

    What worked ?
    Turning the ball valve that supplied cold water to the shower to 3/4 open.
    I am presuming this dropped the cold water preasure and I am pretty sure that the cause of my problem is the cold water presure
    creating intermitent back presure through the mixing valve causing the tkjr to shutdown

    Anyway this works.
    Since reducing the preasure on the cold side I have not had the hot shutoff in the shower once in a month.

    This does nto seem to be effecting my cold supply - atleast not noticiably, only the presure.

    Now I guess I have to put a pressure reducer on the cold water AFTER the takagi, but before the other faucets in the house.
  4. peterc

    peterc New Member

    Aug 17, 2019
    What ended up being the root cause of the issue? I’m having the same exact issue, although it started after about 6 months after getting my Takagi. Tried descaling and messing with the cold water pressure, but issue still persists.
  5. OldSalt

    OldSalt New Member

    Feb 3, 2017
    IT Consultant
    Northern Idaho
    Looks like this thread is about dead, but having seen this problem description while browsing the forum, the first question that pops into my head is, are you using a recirculation pump? If not, never mind, ignore the rest of this post.

    If so, though my system is a Rheem, most system designs call for a check valves between the cold water feed and the start of the hot water system, and another check valve between the return feed and cold water tank intake. Those valves are to prevent hot water from entering the cold water supply line, and cold water from entering the recirc hot water return line. If the later fails, cold water can backflow into the hot water line, with the hot water valves at the end of the run receiving the cold water first. Could be a shower, a sink, whatever.

    In my case, the check valve was fouled by lime scale debris from the hot water return, keeping it open, flooding my hot water return line with cold water, causing my wife to scream and curse the husband who installed "that *@*!##$ tankless hot water heater". (City water gets ice cold in Northern Idaho in the winter, too, an "electrifying" experience, so I forgive her.) :) The symptoms were inconsistent, even mysterious. I'd have hot water flowing freely to the sink across from the shower putting out ice cold water, and since I installed the plumbing, I knew they were from the same 3/4" line feed, with branches in virtually the same location on that pipe. Symptoms varied by inline water pressure. Removing and cleaning the valve might work, or you might have to replace it. I've done both. Root cause, if this happens, is hard water. A water softener may fix the problem. I ultimately solved my problem by adding a water filter on the out-take side of the hot water tank, preventing tank debris from entering the hot water line. That also protected all of my faucets and shower heads from fouling as well. I'd recommend it to every tankless hot water system as a precaution. Though I've had a few persons on this forum swear that their water is as pure as it was first created, in my personal experience, all hot water tanks everywhere produce at least some scale, and that scale enters your hot water line, fouling everything down flow from the hot water tank. (Regular hot water tanks don't seem to have that problem. The out-take hot water supply line is at the top of say, a 30 or 50 gallon conventional tank, and the sentiment sinks to the bottom of the tank.)

    Hope this isn't off-topic. I've got an in depth thread somewhere on the forum documenting some of this. Feel free to me a message if this is relevant to your situation, and you have any questions. (I don't frequently scan this forum.)
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