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neato5oh 10-07-2006 05:41 PM

Lennox G11Q3E-110V-6 gas furnace

Iím having a problem with my (ancient) Lennox G11Q3E-110V-6 gas furnace. Whatís happening is:

Comes on (spark, pilot, main burners come on almost simultaneously)
Stays on for 1 to 45 seconds (measured: 19,2,12,24,12,14,1,7,45,19 seconds)
Goes off for between 6 to 52 seconds (measured: 50,10,24,26,17,6,10,19,52 seconds)
Comes back on (spark, pilot, main burners come on almost simultaneously)

And on and on and on. Sometimes thereís a rapid click-click-click (of the valve?) when itís off.

Iíve looked around in there and I see thereís a Johnson G60QHL-1 ďPROVEN PILOT CONTROLĒ (maybe not so proven?). That appears to control the gas and pilot valves. Thereís also a ďcam-statĒ thatís currently set to 110 ( think this controls when the fan turns off)

Iíve lived here with this furnace for 9 years and it was pretty good for the first 6 or so. I remember this problem from last year, but I made it through the winter somehow. I tried removing the pilot assembly and cleaning up the thermocouple last year and I thought that helped. Did that again today, but it did not seem to make a difference.

Any suggestions?

Thanks very much,

Judson 10-08-2006 03:22 PM

I think you have a flame rectification type
I looked up some of the numbers in your post and I think you have a flame rectification type flame sensor. I believe you also have an intermittent pilot (as opposed to direct ignition). This is the most common type of residential gas furnace these days. You should make sure of this but assuming that it is...
There is no thermocouple in these systems. The flame is sensed electically. There are one or two electrodes for spark and sensing. Usually just one elctrode is is used for both spark and sensing.
In these systems only the pilot flame is sensed. The control logic assumes that if the pilot is lit that the main burner will lite.
Its sounds like the pilot is not being properly sensed.
Make sure the pilot is not clogged and that it is properly adjusted.
Look up flame rectification on the internet.

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