gas furnace not firing up

patandmaryNovember 16, 2012

We just replaced our older heating system with a new Trane dual-fuel system. Everything has been fine, but we have a problem now. With the thermostat on Auto system, we understand that the heat pump will work until it can't, and then it will call up the gas heater. But sometimes the gas heater doesn't want to engage. We can hear it trying to fire, and there is an interesting yellow glow that we can see in the heater (looking through the grill work). But it doesn't always fire up, and last night the furnace tried for a good five minutes before the decision was made to manually change the thermostat to Emer. heat. When that was done, the heater fired up just fine, and cycled off and on during the night to keep the house temp. where we wanted it. We have had the technician out, and he has checked the system and declared that everything is set okay. An interesting note: our older system, which was not a dual fuel system, but just a gas heater plus an AC, had the same problem toward the end of its time with us. Could we have a gas pressure problem, instead of a heater or thermostat issue? Many thanks for any ideas.

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Speaking as a non-PRO, most references to 'auto-system' that I've seen refer to the thermostat to have the ability to switch between heating and cooling, where the climate has high daily temperature swings. Are we talking about system heat/blower auto?

Is the thermostat one that will control a heat pump? If it is a proper stat, with dual fuel kit installed, it should work. Did you try setting the stat to (plain) heat?


    Bookmark   November 16, 2012 at 3:20PM
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Yes, our auto-system does allow the system to switch from heating to cooling b/c of temp swings. Our system did that switching well during the early fall.

Not sure what you mean by 'system heat/blower auto'. The fan is on auto, and under the System heading we have Emer. heat, heat, off, cool, auto. We have put the system on "heat" instead of "auto" at this point, to see if that is the correct way to solve our problem. Thank you.

    Bookmark   November 17, 2012 at 11:04AM
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"We have put the system on "heat" instead of "auto" at this point." Yes, that is what I referred to.

On my stat, there are 2 blocks with options: One, (system) for heat, cool, auto; and (fan) for auto, on, program.

I guess you'll need some cold(er) weather.


    Bookmark   November 17, 2012 at 1:50PM
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i thought new HE furnaces had sealed combustion chambers? how is it that you can see the glow of the igniter? that seems odd. maybe i dont know how new high efficiency units work.

    Bookmark   November 20, 2012 at 4:19PM
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A typical HE furnace has two sections; one, the blower section; the other, the heating section. They are separated and sealed from each other, as well as the 'atmosphere'.

Access is gained by removing front panels on each section. In a (true) sealed combustion unit, the burners receive their combustion air from outside, if piped. The igniter is positioned so that the flow of gas can be lit.

Has your problem been solved?


    Bookmark   November 22, 2012 at 9:27AM
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Since we have changed the setting to "Heat", and it's not on "Auto" any more, things have been good. So maybe it's more of a system hiccup than anything else. We'll resume the "Auto" setting in the late spring/early summer, so it can do its flippy thing as it needs. Thank you for all comments. Talking about it has helped a great deal.

    Bookmark   November 26, 2012 at 9:40AM
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This is really strange. If you see a glow in the sight glass that means that the ignitor is glowing, waiting for pilot gas from the gas valve, and it is not coming. I had the same problem, and mine WAS a gas pressure problem. Mine would light off after about the third try, so I suspected low presure. Upping the pressure a bit solved the problem. I am not a pro, but I suspect that something is wired wrong between your furnace and your thermostat. Did you try killing the power and rebooting the system with it on auto?

    Bookmark   November 28, 2012 at 12:35PM
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