Takagi Jr Troubleshooting

Discussion in 'Tankless Water Heater Forum' started by duff, Jan 15, 2010.

  1. duff

    duff New Member

    Messages:
    3
    Location:
    Wisconsin
    The unit is set up for hydronic heating of a basement slab. Circulator is TACO007

    The heater was installed in fall 2007 and run in winter 2008. Performed well.

    Shortly after start up in 2009 I found the unit would not restart after the temp dropped below the thermostat set point. It would restart if I unplugged it (elec) and plugged it back in.

    After this happened a few times I called the HVAC guy and he insisted it needed to be descaled. In the meantime the heater failed to a point that it would not restart even after unplugging it (elec). The flame comes on for one or two seconds then shuts down. The water goes cold and unit powers down completely.

    I recirculated a sulfamic acid solution through the unit for an hr. A small amount of scale was removed. Not enough to use up the acidity of the solution.

    Heater does same thing. Fires up, runs for a second or two then shuts down

    Any ideas?

    I have the HVAC guy scheduled (same as installer). but its been 4 weeks since original call and he is set on it being a scale problem.
  2. what kind of acid????

    what kind of acid did you run through that unit??:eek:

    sulfamic acid ??


    I dont think you are supposed to run anything stronger than
    vinegar through a Takagi, not even CLR...
    only strong vinegar or they might decide to
    void the waranty due to your decision........


    I dont think the hvac guy needs to know about this
    Last edited: Jan 15, 2010
  3. Dana

    Dana In the trades

    Messages:
    2,804
    Location:
    01609
    The likelihood of this being a scale problem is remote IMHO. If this is a "closed" system (as opposed to and "open" system that uses potable water as heating water, which is allowed in some places, but never a good idea), the amount of scale that can build up is self-limiting since there isn't constantly new minerals being introduced to the system. Whatever was going to condense & acrete to the heat exchanger did so within the first few hundred hours of operation, since there are at most a couple 10s of gallons of water you're dealing with.

    If there's a remote control installed on the unit (?), it should be reporting a code which would indicate a fault condition # to give you a clue.

    Odds are pretty good that it's a dirty flame detector, and the controls are tricked into "thinking" that it failed to ignite, in which case it can be revived by buffing it up lightly with a Scotchbrite or similar not-too-abrasive fine plastic type scouring pad. (Don't use steel wool or sandpaper if you can help it.) If you don't already have it, download the manual, unplug it, and carefully disassemble it to the point where you can gain access to the business side of the flame sensor. (See the exploded diagram on p.24, follow to where item 105 attaches to the flame sensor on the burner unit.) Odds are it's got a bit of soot/discoloration on it, that once removed, will get you back on the road again.

    Sulfamic acid isn't ultra-strong- not a strong as sulfuric acid, but it all depends on the concentration use. It's usually mixes at room temperature to significantly stronger than standard solutions of white vinegar used in food. The typical descaling solutions have a PH of 1.5-2, whereas 5% acetic acid (vinegar) is much weaker, at a PH of 2.4. It's a copper heat exchanger, which can be fairly sensitive to acids, and you have converted some of it to copper-sulfate in the process. (Of course, pickling in vinegar converts some of the copper to copper acetate too, but it's a matter of the concentration and duration of the rinse.) Sulfamic acid is used often for removing rust & scale from less-sensitive cast iron, but I'd never run it through copper in anything but a very dilute solution. White vinegar sold as food enhancer is already fairly dilute, and far less likely to damage the unit.
  4. duff

    duff New Member

    Messages:
    3
    Location:
    Wisconsin
    Thanks Dana. It was the flame sensor. Fired right up after buffing with green scour pad.

    Unfortunately the gasket that holds the flame view glass plate crumbled. I called Takagi and ordered 2 at $1.70 each...So I wasted some money on a recirc pump and hoses. But at least I can fix a a flood now

    Makes perfect sense about the scale and closed water too.
  5. Dana

    Dana In the trades

    Messages:
    2,804
    Location:
    01609
    Sounds like it's time to lose that HVAC guy's number, eh? (Seems he has nothing but bad instincts, and worse advice!)

    It's a bit on the early side for the flame detector to have crudded up, but if it's sucking air from inside their are many air contaminants that can contribute to it. But at least now you know the drill, should the symptoms recur.
  6. duff

    duff New Member

    Messages:
    3
    Location:
    Wisconsin
    Would the fact I run LP vs nat gas be a reason the sensor fouled early?
  7. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Not really unless you ran out. On occasion people have reported bad burns at bottom of tanks due to moisture and odorants added.
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