well thank you all that have posted fixes for the lennox no start problem. i have been having problems the last 3 years with my lennox g23 furnace, the furnace is 12 years old and main module brd was replaced about 4 years ago because it had burnt trace on pcb at the center relay.well i just cleaned the flame sensor and i have not seen it start up as fast as it just did(it took about 5 seconds after the pilot light came on, before it would take 15 to 20 seconds to light. only took about 10 minutes clean the sensor with 200 grit sandpaper.