How to light the pilot light on an old furnace
Old furnaces often have hidden pilot assemblies or switches that fail to ignite even when following standard steps like holding the gas switch and hitting the igniter. This leaves homeowners struggling to figure out whether the system requires manual lighting or if there is a deeper mechanical failure, often forcing them to call a technician.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from October 2026.
- This comes up 15.4× more often in r/hvacadvice than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Calling an HVAC technicianDid this help you?
- 2Holding down the gas control knob on the pilot setting for extended periods to purge air linesDid this help you?
- 3Disconnecting the gas line to manually confirm gas flowDid this help you?
- 4Turning off the gas supply valve overnight out of cautionDid this help you?
- 5Turning off the gas on the line, removing the top middle Phillips head screw to access the hidden adjustment screw underneath, and turning it clockwise.Did this help you?
- 6Replace the HVAC air filter before starting the furnace for the season and change it every 3 monthsDid this help you?
- 7Have an HVAC professional inspect and clean the system twice a yearDid this help you?
- 8Clear furniture away from supply and return air ventsDid this help you?
- 9Test carbon monoxide detectors before turning on the heatDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Just bought my first house over the summer so I’ve never done this before.”source ↗
“Do I just need to light a pilot light? Or should it ignite automatically?”source ↗
“I turned back on the gas valve, turned the furnace valve switch to pilot, held down the red gas switch, and hit the igniter. Nothing.”source ↗
“I opened some panels up and I can't even see where i'd try to light it manually.”source ↗
“Any help before I shell out money for a tech?”source ↗
“I can light it OK, but how do I adjust it?”source ↗
“Thanks! I've seen videos where the guy lights the pilot and then turns the pilot adjust screw while monitoring the flame”source ↗
“Finished setting up the new 50-gal, 40,000 BTU water heater last night, hooked up the water lines, filled the tank, tested the TPR valve, connected the gas line, and then proceeded to light the pilot. Nothing, nada, zip.”source ↗
Where this came up
People with this problem also raised
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- 17Furnace lights up then immediately goes out
- 8How to maintain an older home chimney yourself
- 2Furnace making popping sound and flame flickering