Troubleshooting Payne propane furnace blower fan constant but no heat

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Agree, IF it has an inducer. From the picture, there was no evidence of one. It looks like an older furnace.

Yes, usually after a delay of a minute or so

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About time!
Christopher A. Young Learn more about Jesus www.lds.org .
Agree, IF it has an inducer. From the picture, there was no evidence of one. It looks like an older furnace.
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A few points.
The OP gravity draft furnace doesn't have inducer fan.. sip your martinis, don't gulp them. Blower all the time might be a bad fan limit switch. Ten commandments, not twelve. The "glow bars" I've seen have been 110 VAC. We refer to her as Virgin Mary, not Mary with the Cherry. You don't sound like you know furnace troubleshooting. We refer to Father Son and Holy Ghost, not Dad, JC, and the spook.
Christopher A. Young Learn more about Jesus www.lds.org .
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Probably a bad idea to just start replacing parts.
It's strange that the main blower starts up at all, because normally it doesn't start until after the flame is detected by the flame sensor and the burners start (so it doesn't blow cold air), unless you have the fan always on at the thermostat.
The sequence should be:
1. Draft inducer fan starts up and closes switch (via suction) so the controller knows that the draft inducer is operating and it's safe to light the burner. You can check this with an ohm meter, or jumper across it to test it (however it must be open when the furnace starts, then closed after the draft inducer fan starts, you can't jumper it closed before the draft inducer fan starts).
2. Glow plug heats up (or spark ignitor starts sparking). You can check that a glow plug is getting power with a voltmeter (should be 24VAC) and you can see it glow red. A spark ignitor should make a noise.
3. Gas valve opens and burners ignite. Audible thunk as the solenoid is activated. Controller knows that the burners are lit by looking at the flame sensor and will close the gas valve after a short time if there is no flame. You can test the gas valve by turning off the gas to the furnace, unplugging the wires to the valve, and connecting 24VAC or so to the valve from a small transformer. If you hear a thunk then the solenoid is activating and the gas valve is probably okay.
4. Main blower starts up.
If one of the flame-out sensors is bad (open) the gas valve won't turn on. There are usually three or four flame-out sensors in series. If there's a crack in the heat exchanger then flames can shoot out the front of the furnace and the flame-out sensors will shut off the gas.
When my furnace broke a couple of months ago it was an intermittent gas valve.
When my friend's furnace broke last month it was an intermittent draft inducer fan switch (sometimes it's just a clogged suction hose, but this time the switch was bad).
If it's an older furnace with relays on the controller board you can hear the relays click as various things are activated. The draft inducer fan relay will click, the ignitor relay will click, and the gas valve relay will click.
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