I have a Lennox G60UHV furnace that intermittently will not start heating when the thermostat demands heat. It will however heat 45 minutes after the initial demand. This appears to be a WatchGuard issue. However, there are no indicators on the control panel that the system is in WatchGuard. This usually occurs when the attic tempature is below 55 degrees. When the system is warm, it functions normally. The Flame Sensor and Flame Ignitor all are within limits. Does anyone have any ideas as to what may be causing this behavior.

If you Google "Lenox WatchGuard problems" you will find 31,500 hits. Appears that system has been an issue with many posters.