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Thread: TK-Jr Issues--resolved?

  1. #1
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    Default TK-Jr Issues--resolved?

    (CROSSPOST--moved to its own thread)

    I have a TK-Jr that heats both the radiant flooring and domestic hot water. It usually works fine (great, in fact, considering the size); however, in the mornings, after it has been working a while to heat the house, when someone tries to take a shower, the unit shuts off. The diagnostic led blinks three times. Resetting it by cycling power resolves the problem (until the next morning). The unit is inside and I don't have the controller with the diagnostic codes.

    UPDATE--Upon checking the unit BEFORE it shut off, I also discovered the LED was flashing FOUR times--a different set of problems (the LED inside the unit flashes a number of times to signal a general type of problem, the $100 external controller gives a numeric readout that gives a more specific diagnosis.)

    Anyway, I got Takagi tech support on the phone. Based on the codes, hey recommended that (1) the exhaust be shortened as it was too long (about 20 feet of run and four elbows, each of which is considered 5" of run, so a total of 40" of run, but the unit is only rated for 25" max).

    THey also recommended cleaning the unit, and emailed me detailed directions. I followed the directions, and sure enough the unit was really full of dust. This is likely due to the fact that there was a a lot of dust (plaster and other crap) in the air when the house was being constructed. Also, the gaskets were destroyed in the process. I made replacement gaskets from a thin piece of fiberglass insulation, and put it back together.

    As of this morning, the unit has been running fine (about two days). I will have to see how it goes, but if you don't hear from me you can assume the cleaning did the trick. So be aware: the unit (and tankless heaters in general) is clearly an amazing piece of engineering, able to not only heat our house but also provide domestic hot water, in a unit about the size of a large briefcase--but its small size makes it susceptible to dust and dirt.

  2. #2
    In the trades Dana's Avatar
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    Yet another mis-installed tankless!?! I'm SHOCKED! (Not...:-) )

    For the record, was this a DIY installation, or was a so-called "professional" responsible?

    Did you correct the venting issues? (If not, you should.)

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    Dana, the unit was installed by some general contractors who were pretty sharp, but not pro plumbers or HVAC. We made the decision to make the vent longer to avoid having to punch through the metal roof. The unit worked well for a year, but the buildup of dust as a result of having it in service during construction clearly impacted its efficiency--I'm guessing the combination of too long vent and dirt in the unit was the problem.

    The good news is the cleanup seems to have solved the problem, at least it hasn't shut off for a couple weeks (of course, it hasn't been bitter cold, and the kids had last week off so there weren't showers first thing in the morning).

    You're probably right--would shortening the venting make the unit last longer, or be more efficient? Fewer holes in the (metal) roof are obviously better, but it's just a carport. I'll probably work on that in the spring.

    PS We also noticed the water is considerably hotter--a result of cleaning the heat exchanger, no doubt. Hopefully we'll also see a savings in fuel.
    Last edited by activa; 02-21-2010 at 06:51 PM.

  4. #4
    In the trades Dana's Avatar
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    These things are designed to operate within a certain range of backpressure on the venting. Too much venting slows down the flue exhaust, reducing the turbulence on the heat exchanger, leading to increased stack temps == lower efficiency. Above some range it might be detected by the controls, but in the meantime it's lowering your efficiency slightly, and will have higher carbon monoxide in the exhaust since it'll be running slightly richer in fuel to air than designed.

    It's in an open carport?

    Getting the gunk off the heat exchanger probably WILL show up in your heating bills, if you measure fuel consumption correlated against heating degree-day weather data. I'd imagine by the time the thing is spitting out codes and shutting down the combustion efficiency is down in the low-70s rather than the 83-86% it would normally be running. (Never tested this- just a guess.)

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