I have been having the same problems with my Lennox G23 gas furnace. If you read back through this message board, LOTS of people have been having the same problems (look here: http://www.renovateyourworld.com/wwwboard/messages/72462.html). After much time and research, it appears that the problem is with the Johnson Controls Ignition unit. After many tries, Lennox finally moved to a Honeywell model that apparently is much more reliable. Search for Lennox part # 53L90. I have found it for $144. It is a complete relacement unit for the Johnson model. Order and replace yourself or have a neighbor or someone you know who has worked on gas furnaces before do the replacement. I have wasted much $$ on service people and they cannot determine the problem.