Trying to help stepson with a "gas pack" HVAC unit (a packaged unit that sits beside the house and incorporates an A/C and a natural-gas furnace). The gas furnace does not come on reliably.
The furnace has 3 burners, each an orifice in the side of a length of black pipe. The igniter lights the first one and then the flame jumps to the 2nd and then the third. The safety thermocouple/thermopile is on the 3rd burner, so it shuts the gas off unless all three light. This appears to be the normal behavior.
What often happens is that the first burner lights, but the flame fails to spread to the 2nd and 3rd burners and so the system soon shuts off; after 3 tries it gives up. If he cycles the thermostat (which I assume resets the low-voltage control circuitry in the unit), and does that several times, eventually it comes on properly.
We can't figure out what is causing this behavior. He did a half-assed attempt to clean the orifices but he said they didn't appear clogged. I guess the black pipe could be partially clogged, but if that's the cause why does it sometimes come on exactly the way it's supposed to (the three burners fire up in quick succession, and the 3rd has just as good a flame as the first) ? Could it be the valve is faulty and sometimes doesn't let enough gas pressure through ? Bad gas pressure to the house ?
Googling suggests low pressure and/or clogging. It just doesn't make sense to me that it fires up perfectly ... sometimes.
The furnace has 3 burners, each an orifice in the side of a length of black pipe. The igniter lights the first one and then the flame jumps to the 2nd and then the third. The safety thermocouple/thermopile is on the 3rd burner, so it shuts the gas off unless all three light. This appears to be the normal behavior.
What often happens is that the first burner lights, but the flame fails to spread to the 2nd and 3rd burners and so the system soon shuts off; after 3 tries it gives up. If he cycles the thermostat (which I assume resets the low-voltage control circuitry in the unit), and does that several times, eventually it comes on properly.
We can't figure out what is causing this behavior. He did a half-assed attempt to clean the orifices but he said they didn't appear clogged. I guess the black pipe could be partially clogged, but if that's the cause why does it sometimes come on exactly the way it's supposed to (the three burners fire up in quick succession, and the 3rd has just as good a flame as the first) ? Could it be the valve is faulty and sometimes doesn't let enough gas pressure through ? Bad gas pressure to the house ?
Googling suggests low pressure and/or clogging. It just doesn't make sense to me that it fires up perfectly ... sometimes.
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