How do I reset a Lennox furnace?

How you reset a Lennox furnace like ML296V, EL296V, and SLP99V to clear error codes and control glitches involves power cycling and thermostat reset, as there is no single dedicated reset button like oil furnace. First method is hard power reset that works for all Lennox furnaces: set thermostat to off, turn off power switch on side of furnace that looks like light switch, turn off breaker at electrical panel that supplies furnace, wait at least 30 seconds to 1 minute to allow control board capacitors to discharge and clear memory and error codes like E codes on iComfort thermostat, turn breaker back on, turn power switch back on, set thermostat to heat and temperature 5 degrees above room temperature, furnace should start ignition sequence with draft inducer motor running, then igniter glowing, then gas valve opening. Second method is thermostat reset: if using Lennox iComfort S30 thermostat, press and hold menu button for 5 seconds to reboot, or remove thermostat from wall for 30 seconds. Third, check and press rollout switch reset if tripped: remove lower front panel, find small device with red button near burner box, press button that may have popped out. If furnace has condensate drain clog, clear drain as high efficiency furnaces trip pressure switch when drain blocked. Reset clears electronic glitches but does not fix mechanical failures like failed igniter at 100 to 200 dollars or flame sensor dirty.