Takagi Flash T-K2 intermittently not heating

Discussion in 'Tankless Water Heater Forum' started by fmack12, Jul 11, 2012.

  1. fmack12

    fmack12 New Member

    Messages:
    3
    Location:
    sacramento
    Hello,
    I have a TAKAGI FLASH T-K2 tankless hot water heater. It is 9 years old.

    Intermittently: the water won't heat, or the water will start to heat and then stop heating, or it takes an escessively long time to heat. This happens at the faucet furthest from the water heater, which is a kitchen mixer valve faucet. The faucet worked fine for the first 9 years. Rarely, it has happen at other faucets - which have a dedicated hot valve.

    There is not a numeric error code panel on this unit; however, when the water is not heating the RED LED light is FLASHING and the GREEN LED light is OFF.

    The troubleshooting manual for this issue indicates this could be the: Igniter, Flame Detector, Main Gas Valve or Pre Post Check.
    When I unplug the unit and plug it back in at this time, the flame fires and everything works.
    This indicates to me that the Main Gas Valve is not the problem.

    Thus far I have cleaned the input water filter and flushed the system with vinegar, which turned the vinegar a light blue. I have also tested and there is not a plumbing cross flow.

    The toggles are set as follows: (for 122°)
    113 on
    104 on
    NG on
    LP off

    OUT off
    blank off
    IN off
    176 off

    Step by step instructions are always a plus. How do I proceed to fix this problem?

    Please Advise, Thanks.
  2. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    It's easier to debug if you hook up the compatible remote so you can read the actual error code.

    On units this old flame-sensor varnish/crud is always suspect. Cleaning it up with a plastic scouring pad like a Scotch Brite (and NOT SANDPAPER) will often do the trick. Turn off the power and the gas to the unit before pulling it apart, but it's not a big project. Once you've done it once it's even quicker/easier to do again, if need be. (Air contamination issues make this an annual ritual for some installations, but if yours made it 9 years without a problem it's likely that you'd go years between cleanings.)

    Flow detector wear could be an issue too if it's only happening with lower flow faucets. IIRC the T-K2 needs to detect a bit over 1gpm to light up, and will flame out if flow drops below ~0.8gpm.
  3. fmack12

    fmack12 New Member

    Messages:
    3
    Location:
    sacramento
    Dana, thanks for your reply. I will clean the flame-sensor, then install a Temperature Remote Controller TK-RE-02 for the error code if that doesn't work. It has been 105° here lately, and this thing is in the attic, so I am going to wait till it cools down a little before I get to this project. May take me a while, but I'll be back in touch. Thanks again.
  4. fmack12

    fmack12 New Member

    Messages:
    3
    Location:
    sacramento
    Hello Again,
    Cleaning the flame sensor seems to have done the trick - and it wasn't really visibly dirty or gummed - but the scotch bright pad has things working correctly . . . for now.
    Thanks for your help. :cool:
  5. Corbino

    Corbino New Member

    Messages:
    3
    Location:
    Milwaukee
    Dana, I have a similar issue going on and tried the flame sensor cleaning above, but no luck. I'm only having the problem with one shower in the house. Thoughts?
  6. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    "I'm only having the problem with one shower in the house."

    If it works normally when other hot water taps are opened and only craps out when that shower is running, it's almost certainly an issue with the mixing valve in the offending shower, not in the tankless. The anti-scald valves develop leaks between the hot & cold sides, and when that happens the pressure drop of the heat exchanger in the tankless can cause all sorts of odd behaviors.

    Do you have the RE-02 remote, which will at least spit out the error code?
  7. Corbino

    Corbino New Member

    Messages:
    3
    Location:
    Milwaukee
    Thanks for responding! I thought the same and replaced the mixing valve in that shower yesterday as well. I watched the unit when the shower requests hot water and it fires then stops right away. I also tried removing the shower head thinking it was reducing flow, but that didn't help. All other faucets get hot water, even the sink in the same bathroom as the shower (sink is actually a little further away). Other ideas? I do not have a RE-02 remote.
  8. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    It's clearly a plumbing-related issue if it only happens with one of the hot water taps, and fails reliably on that tap. The anti-scald portion of the think valve that is the most likely culprit- what kind of shape was the old one in?

    When the shower draws cause the failure, does it give you the blinky-blinky LED code as it hangs up? If yes, what it the blink pattern? I assume you already have the manual? See page 16 for interpreting the LED blink pattern.

    If you plan to own the thing for awhile, it's always worth installing the remote for debugging and re-setting the thing, since the codes are more specific.
  9. Corbino

    Corbino New Member

    Messages:
    3
    Location:
    Milwaukee
    Glad you were so confident in your thinking! I swapped the NEW mix valve with one (9 years old) from another shower in the house with the same faucet and the darn thing gave me hot water. What's weird is I put the valve that gave trouble in the other shower and that works now too. Is that due to the closer distance to the heater?

    My mornings just got easier. AWESOME assistance on this!
  10. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    It's possible that the pressure differential across the anti-scald is different with different plumbing routing. But if the thing worked for awhile then crapped out in it's old location, it's probably going to eventually exhibit wierdness in the new location.

    It's also possible that scaling on the water side of the heat exchanger in the tankless is contributing to it by increasing the pressure drop across the tankless. If you've NEVER descaled the thing (in what, 8-10 years of service?) it's probably worth giving it the 30 minute pumped vinegar rinse. (There are several YouTube videos explaining how to descale a tankless.)
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