Had a call today on a Lennox Pulse. M# G21Q3-80-1. S# 5893F05132. HO said that furnace take long time to get going in the morning. Would lock out.(???). They would reset by t'stat and eventually fire and keep running. Of course when I arrived the system was running fine. Checked the diaphram, was dirty. System runs on LP and had 9"w.c. from a tap on the outlet side of the gas valve. Tap had been bored into a 90. The pressure would start at 9" then decrease to about 6.5" once it ignited. Unsure if this is OK with LP. Also pulled the flame sensor plug and ingnition plug with the special wrench. Real bugger since I'm right handed. Although the unit is from '93 the plugs were OK yet I cleaned them anyway. Unit lit off for me every time. Took a CO reading with my UEI meter outside at the termination. Read 9 ppm. Figure OK. Went back inside and took a reading in the plenum and got 1 (one) ppm. Plan on coming back in several days to do a pressure test on the hex. Although the system was igniting and running while I was there, could not figure out what was causing the lock out. ANY THOUGHTS ??? I have not worked on many Pulses.