Typical/Expected Fuel air current measurement

[Conde]

I have a Takagi T-H3J-DV water heater in a domestic radiant heating application. I am getting the error code 391 (Air-fuel ratio rod failure). I have cleaned and replaced the sensor multiple times but the issue seems to come back intermittently. I did put the heater in diagnostic mode and was able to read the current value on the air-fuel rod. I was measuring 7 µA on a brand new sensor with the unit operating is steady-state conditions.

My main question is, what would be an expected current value? The range on the diagnostic mode is 0-999 µA but that does not tell us much. I have reached out to Takagi to as what value/level of current would set error code 391 but I am not hopeful for a reply. I would assume the fault has some level+time+hysteresis type value.


Thanks, I love this forum for the helpful answers!

 

[John Gayewski]

These are junk heaters. I was working on one with this same issue not long ago. There is a number you can call and the tech was somewhat helpful. You need to measure the gas to make sure the pressure drop is within spec. I haven't heard anything about the one I was working on, but I had ordered a new set of gaskets to take the burner box apart and clean it if it continued its issues.

My recommendation was to get a different heater as it had never been cleaned and it was 10 or more years old.

How old is this heater?

 

[Sponsor]

 

[Conde]

This unit is 8 years old. I did take the combustion chamber apart this summer and cleaned it pretty thoroughly. I will try the Takagi service number as well.

 

[Conde]

I called the Takagi service number and it comes up as AO Smith which apparently owns Takagi and just about every brand as well. They were somewhat helpful but not detailed. I wanted to know the Air-fuel limit that sets code 391 but he did not know. Just said that short cycling and long duration firing can lead to soot buildup so.... Super helpful.

 

[Fitter30]

.5 to 10 microamps uA common readings 2 to 6 their info > 5uA
Has the burner been setup with a analyzer? Or taking combustion air from space like a beauty salon or one that uses chemicals. The flame rod can be cleaned with a scotch brite pad. Appendix A #3

https://www.google.com/url?q=https://www.takagi.com/media/27167/T-H3-Maintenance-sheet-68A166-1.pdf&sa=U&ved=2ahUKEwju7bOu5YP9AhWSkYkEHSXXBdIQFnoECAIQAg&usg=AOvVaw3O9QTHA5aoR4T2NaroKTFn