XE80 intermittent lighting

My furnace XE80 Gas is not always lighting. I hear it start the inducer pre-heat the HSI then light. I hear the flame light. Then it will shut it right off. It will do this once, maybe twice. Every so often it will try 3 times then lock out. Some times it lights fine the first time.

I was able to get the code the last time it locked its self out and it was, "system lock out, no flame"

I have replaced the flame sense rod and still have the same issue.

This problem seams to be getting worse with time. I just went through a process of 2 lockouts in a row, then it lighted fine.

I have now search 2 forums and really cant find what i need to check next. I don't want to call the furnace guy out yet because i cannot reproduce the problem all the time.

Any help is greatly appreciated.
Thanks
Dustin

 

As a quick first step check the ground to the control module.
The flame sensor uses the ground of the furnace as a return path.
You may have a corroded terminal on that module or sometimes where it's attached to the frame of the furnace is rusted/corroded.

The next step in checking the flame sensor circuit requires a Voltmeter capable of reading DC microamps.

 

How do i check that... i know my way around a multimeter. looks like ill be up tonight nursing this damn thing. Just did a lock out again.

Its so frustrating because its heating fine, as soon as i go to bed, it will fail to stay lit.

 

Locate the flame sensor. It is connected with a single slide off connector.
Remove the wire from the sensor.
Connect one meter lead to the flame sensor.
Connect second meter lead to wire that was taken off of sensor.
You're putting your meter in series with the flame sensor.
Set for DC microamps. It's going to be under 10 microamps.

Fire furnace and read meter.
The meter will only read when the flame is present.

 

OK thanks, just trying to understand this circuit.

So when there is flame, the control board needs to see X number of amps from the flame sense rod?

because the flame heating the rod will produce current, (trying to remember back to the old physics class)

 

Check out this link for a good description of that circuit.
It's a link to a pdf file.


http://www.google.com/url?sa=t&rct=j...55534169,d.dmQ

 

Are you sure that ALL the burners are igniting? Have you removed and cleaned the burner faces and crossovers?