High fire pressure switch is cutting out after about a min.
I checked pressures with a monometer it does go down after the furnace heats up for awhile. I checked all over the heat exchangar for cracks but had no luck. I would like to go back and take apart the collector box area to see if there are any problems in that area.
When the G32's first came on the market I had one do almost exactly the same thing. I changed the circuit board and it still had problems. The problem with that furnace was a improper ground, just thought I would throw that out there, it is an easy thing to eliminate as the problem or correct if it is.
Call Lennox Customer Support @ 1-800-453-6669. Have the entire model and serial numbers ready. Ask if this was one of the units that had the combustion blower motor recalled for that very same problem. I must have changed out about 20 or so due to the very problem you are describing.
Yes I did go through tech support out of Texas we have it narrowed down to pressure dropping as the furnace heats up. When you pull the vent pipe off it is even more free flowing So the furnace combustion area is sucking in fresh air from somewhere.