Takagi T-H3 - occasional ignition failure (code 111)

[David Hollman]

I have a Takagi tankless water heater that has had 4 failures to ignite over a period of 1-2 months.

It is a T-H3-DV-P which burns propane and has outdoor intake & exhaust.

In each case when I discovered the problem it showed error code 111. To remedy the issue all I needed to do was turn it off & back on using its onboard power button. In one case this worked after a few tries, in all other cases it worked immediately. (Not sure if there was some time delay involved in those cases which worked right away?)

I've read about this error code including on this forum, and there is Takagi documentation about how to diagnose it. But the cases I've read about seem to assume the problem is persistent. As in, you're supposed to check certain voltages literally while the unit is trying to fire up (if I read it right).

In my situation the intermittency makes me unsure what to do... but I would like to proactively diagnose the problem before it gets worse. But I can't reproduce the failure at-will.

Maybe the intermittent nature is itself a clue to what might be wrong?

The documentation has this summary:

Error code 111 (LED three times flashes) Problem: The ignition fails.
Solution: Ensure the Hi-Limit switch runs properly, and the wires are not loose or damaged. Clean the flame rod from soot and deposits and make sure the computer board is not damaged and the heat exchanger is not leaking.​

Thanks for any advice!

 

[Dana]

If the flame sensor has developed char or varnish on it it can cause that sort of symptom. Cleaning it off with a soft plastic scrubber (eg Skotch Brite) is a good idea. Don't use sandpaper or hard abrasives to clean it, or the fine surface scoring will make the problem recur more frequently.