We have a Lennox 10 gcs external gas unit. When you turn on the therm, the motor starts up. If you go outside and listen to the ignitor you can hear it tic, tic, tic for 3 cycles, never lighting and then the unit will shut of completely(the safety feature, of course). If you jump the heater by introducing fire thru the blower, the ignitor will produce a constant spark(like bzzzzzz) instead of the tic, tic, tic and fire up great! Once the temp in the house is reached the heater will stop. Sometimes it will fire back up all by itself, sometimes it will not. Any suggestions would be appreciated!!!! Have already installed a new ignitor, cleaned the flame sensor, and tried a new connection to the ignitor.