When I Googled the manual for this furnace line, it said there were two versions in use as far as ignition goes. One type is what I would call electronic ignition, or Intermittent Pilot. In this form there is NO permanently-operating Pilot Light, and the manual clearly shows for those models that the several gas control valves all have NO "Pilot" setting on them, although there is a pilot flame. It's just like my furnace - not Lennox. When the thermostat calls for heat there is an ignition sequence that starts with a purge wait (to clear any old gas). The next step is powering on an electric arc between electrodes, and this clearly is powered from the 120 V AC supply to the furnace. It CANNOT be done with the electrical supply turned off. (In OP's case the instructions specifically said to turn OFF the electrical supply while lighting the Pilot Light.) The electrodes are placed near a small jet. Once the arc is established a small gas flow comes from the jet and is ignited by the arc, establishing an Intermittent Pilot Flame. This burns for a short period during which it heats up a thermocouple. If that heat does not happen, the Intermittent Pilot gas is shut off. But under normal operation it does heat the thermocouple and after a short time the electric arc is stopped, the main gas valve is opened, and the gas from the main burners is ignited by the Intermittent Pilot.
Now, many of us are used to older systems where there was a permanently-operating Pilot Light that kept a thermocouple warm to verify its function. To start the Pilot Light you had to turn the manual control valve to "Pilot", extend a lit match in close to the end of the Pilot Light jet tube, and push and hold the Pilot Light button. This allowed gas to flow to the jet, bypassing the valve controlled by the thermocouple that, under other circumstances, would NOT allow gas to flow when the thermocouple is cold. Once the thermocouple was warmed up, it was safe to release the button and the Pilot Light would continue to burn. You then shut all the covers up and turned the main control valve to "On". From then on the thermostat could turn on and off the main burner gas supply, and they would be ignited by the Standing Pilot Light.
OP's Lennox unit says it is different in the WAY the Standing Pilot is first ignited. It specifically says NOT to use a match or external flame to ignite it, because it has its own built-in igniter. Now, that could be an electrically-heated hot spot, but the instructions also say to turn OFF all power to the furnace before starting. So the other option is the Spark Ignitor I spoke of. It causes a spark to jump across electrodes near the Pilot jet because a mechanical stress is put on a piezoelectric crystal to generate a short-lived electrical voltage. This requires no external power supply, but the spark only happens once as the crystal is stressed, usually by pushing or turning a knob, often one connected to the action of opening the Pilot Light gas valve. It appears this system had failed, and the service tech's solution, rather than an expensive part replacement, was to ignore the instructions and use the old manual method of lighting a Standing Pilot. Works OK. OP just has to remember for next time NOT to follow ALL the instructions.
OP, your main gas control valve DOES have a "Pilot" position on it, right? This proves that it is NOT the Intermittent Pilot type that re-lights itself every time the thermostat calls for heat. It IS the Standing Pilot Light type, but its automatic ignitor system has failed. So now you just have to light it manually with a match, but rarely.
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