Almost all gas furnaces built in the last 20 years will no longer have a standing pilot gas valve. Older units that require the pilot lite to be manually lit will have the lighting instructions close by, and a pilot depressor knob (usually red) on the gas valve. The Valve control must also be turned to the pilot position before depressing to release gas through the pilot tube.
The pilot burner should only have one flame sensing rod (thermocouple) in the pilot flame space. If there appears to be a second rod or probe, then the system is set up for spark ignition and pilot lighting cannot be safely done manually.
Another way to tell if there is spark ignition or direct ignition on a gas furnace is to listen to the start-up sequence on a call for heat. The first thing that is heard is the draft inducer fan (or venter motor) that will pressurize the vent piping by drawing the combustion gas products and move them out through the chimney/vent pipes. Spark ignition on some models will lite the pilot and follow up with the main burner, whereas a direct fired gas valve with hot surface ignition (glow coil) will go straight to main burner without pilot.
So as a rule, all high efficient and most mid efficient gas furnaces will have a draft inducer motor and never a need to manually light the pilot.
When lighting a standing pilot, a flame sensor with a strong signal should lock in the pilot flame after just a few seconds of purge or hold time. If you are waiting for more than 10 seconds you should consider replacing the flame sensor or pilot generator before it fails altogether.
Working on natural gas equipment should only be performed by a qualified licensed person in the trade.
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