Takagi Flash T-K2 intermittently not heating

[fmack12]

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.

[Dana]

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.

[fmack12]

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.

[fmack12]

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.