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Thread: tankless water heater not always turning on.

  1. #1
    DIY Junior Member spreve's Avatar
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    Default tankless water heater not always turning on.

    I have a Tagaki tankless hot water heater and I'm hoping you guys can help me track down an issue. The basic issue is that the hot wate heater does not always turn on when the circulating pumps turn. I've cleaned the filter on the cold water line and disassembled the unit to look for impeedments on the flow switch and cannot find anything. The only way I can get the unit to activate when it does this is to close the shut off on the cold water line just before unit for a quick second then open it back up. When I do this the unit fires right up. At first I thought maybe I was getting a back flow issue and the pumps may be stealing water from the other circuts but that does not seem to be the case. I can turn off the shutoffs on all the other lines and it still will not turn on. Im at a loss here and was hoping you could give me some advice.

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    Most tankless heaters will not turn on unless a set minimum flow rate is met.

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    DIY Junior Member spreve's Avatar
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    I think the flow rate is fine, if I look at the guages on the radiant manifold they are @ or above 1gpm for each loop of the 2 loop and .5gpm on each loop for the 5 loop manifold. I suppose I could look for a mechanical guage to see if I can read flow rate on the 3/4 inch cold water in line just before the heater.

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    In the trades Dana's Avatar
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    It sounds like your using this beastie in an open system hydronic radiant heating application (?).

    What model? Takagi T-K2, KD20 an TK-1 will inhibit firing if the return water entering the unit is ~130F or so, but that doesn't sound too likely here unless it's a staple-up or suspended tube system and you have the output temp really cranked up.

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    DIY Junior Member spreve's Avatar
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    Dana I just want to thank you. Your post reminded me that we had used the tankless this summer combined with the ower washer to clean/degrease the underside of the cars. When I did that we had set the temp up to 140 and never reset it.

  6. #6
    In the trades Dana's Avatar
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    You would normally have more than a 10F delta-T on the heating loops unless you're pumping at monster-rates, but if dropping the temp back to something under 130F fixed the problem just call it a success be done with it!

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