Pellets Not Feeding: After extensive diagnostics, I am stumped!

[Ken1]

QuadraFire 1200i.

After initial pot fill, stove ignites, thermocouple heats up gradually and delivers 3.8mV, but green light never comes on and auger (pellet feed) does not start.
Putting control box in diagnostic mode with appropriate jumpers, combustion blower, ignitor, convection blower, and auger all test run as they should.
When combustion blower is on, it is creating sufficient vacuum to close the vacuum switch (continuity across switch terminals). Vacuum tube clear.
Door closes tightly.
New control box causes no improvement.
Unit has power, so I assume snap disk#3 is OK.
What is left that could be causing this issue?

Stumped. Welcome ideas.

 

[jzm2cc]

I'd try priming firepot with a bit more pellets to see if Green LED comes on during startup and continues to red LED.

if you've replaced thermocouple there is a possibility it was built in reverse so the voltage would be negative and green LED would never come on to allow feeding of pellets beyond initial feed

 

[kappel15]

Is the thermocouple an oem part ? Make sure the ceramic cover is clean inside of any ash and that the thermocouple is touching the inside end of the cover, or it won't read correctly. kap

 

[Ken1]

I'd try priming firepot with a bit more pellets to see if Green LED comes on during startup and continues to red LED.

if you've replaced thermocouple there is a possibility it was built in reverse so the voltage would be negative and green LED would never come on to allow feeding of pellets beyond initial feed

I had tried priming the pot and even with sustained hot flame, no progress to green or red.

Polarity reversal on the newly manufacturing thermocouple is an interesting possibility--hadn't thought of that. Checked and unfortunately still doesn't function. Tried with second thermocouple and same negative result.

Thanks for the suggestions.

 

[Ken1]

Is the thermocouple an oem part ? Make sure the ceramic cover is clean inside of any ash and that the thermocouple is touching the inside end of the cover, or it won't read correctly. kap

Ceramic cover is also new and the 3.8mV during initial pot burn is being registered through the ceramic cover, so it appears to be working properly.

I wonder if old control box is bad and replacement is also a dud OR there is a wiring harness issue (although that seems unlikely and there is no visible damage. Perplexed.

Thanks for suggestions.

 

[gdelmas77]

Ceramic cover is also new and the 3.8mV during initial pot burn is being registered through the ceramic cover, so it appears to be working properly.

I wonder if old control box is bad and replacement is also a dud OR there is a wiring harness issue (although that seems unlikely and there is no visible damage. Perplexed.

Thanks for suggestions.

Did you ever figure it out? I am having the same issue

 

[kappel15]

Hopefully you know someone with a 3 speed control box stove, you can try your boxes in to see if they are good or not. Some dealers have the ability to test them, or try in one of their stoves. kap

 

[Ken1]

Did you ever figure it out? I am having the same issue

Figured it out. While the new thermocouple generated voltage, when I put in a 2nd new thermocouple, the stove started working. So, for one reason or another the 1st new thermocouple was a dud. I suspect it had a defect (e.g., micro crack or defective material) that caused it to take a longer time to get up to full voltage than the control box would allow.

 

[kappel15]

Sometimes if you are too rough with them, putting them in, it can crack the coating. Glad you figured it out.
kap