Having the following problem with 6yr old Lennox G23.

Woke this morning and temp in house was 62degs. Check thermostat and it said heating, temp set on 68.

Checked the unit and both the diagnostic LEDs were flashing alternatively and slow. According to the Diag Sheet, this is "Watchguard - Burners failed to Ignite".

Shut unit down and waited 15mins, performed a restart and unit was working properly, both LEDs flashing simultaneously and slow.

Temp got to preset value 71 degrees and a little later, noticed temp was back to about 67 degrees, thermostat was showing heating, but nothing was coming from the vents, and no flame on the unit.

Check LEDs again and saw the same "Watchguard" failure as above. Shutdown unit and performed a restart, heater kicked on, but now the LEDs are #1 slow flash, and #2 fast flash, which according to the status table is "Low flame signal, check flame sensor".

It seems that the unit works OK after a restart, but after shutting down after reaching the desired temp, it doesn't restart correctly.

Help, its going to be really cold tonight in MI.

Call a service person who has experience with lennox. They are a problem child and have been for years. We refused to service them due to so many problems. We never sold them due to there reputation.

Think I found the problem, contaminated flame sensor. Removed sensor and cleaned it with some fine sandpaper and unit is working fine now.

You got very lucky with that lennox