What is the flame rollout switch for?

californianMarch 9, 2011

I have a Carrier 58wav070-1-12 gas furnace and the induced draft blower motor is not turning. The LED fault code is three short flashes followed by three long flashes (33), which is supposed to mean limit or flame roll out switch is open.

I know the blower is good because it turns if I disconnect the wires and apply 120 volts AC directly to it.

There is also supposed to be a manual reset on some limit switch, but I don't see any switch with a reset on it. And it doesn't say what the limit switch is for or where it is.

Another symptom is the main blower is always running.

My guess is the problem may be the computer that controls everything because the component self test doesn't run.

I guess a defective low gas pressure sensor switch could also inhibit the furnace turning on because that is not tested by the self test.

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johnhvac

In the link below is your operating manual

There is a drawing showing approximate locations for the various limits etc depending if it is a upflow,Downflow furnace etc

The switch is also called a flame roll out switch, if you reset it and it shuts off again, Get a tech in there to determine the cause of the failure. I cannot stress this point enough!

This is from the Carrier Manual

Check the manual reset limit switch(es) located near the
burners. If the furnace has experienced a high-temperature condition due to inadequate combustion air, these switches will shut off the furnace. Reset the switch(es) by pushing the button on the switch. If the switch trips a second time, turn off the furnace and call for service.

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/om58-93.pdf

    Bookmark   March 10, 2011 at 9:33AM
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ionized_gw

Yes, but inquiring minds want to know what it is for.

    Bookmark   March 10, 2011 at 4:35PM
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brickeyee

"Yes, but inquiring minds want to know what it is for."

If for ANY reason the gas flame comes out forward it kills everything.

It could be due to delayed ignition and gas buildup, a partially blocked flue or passages in the unit, etc.

    Bookmark   March 10, 2011 at 6:20PM
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californian

I spent about four hours yesterday researching my problem and flame rollout switches. In case anyone is interested the flame rollout switch detects something called flame rollout, which is where the flame goes somewhere it shouldn't like through a cracked heat exchanger or out the front of the furnace.

    Bookmark   March 10, 2011 at 6:27PM
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berlin

well, it won't sense it if it goes "through" a cracked heat exchanger, but when the blower kicks on, if your heat exchanger has a large enough perforation, the conditioned air blower will blow the flame back onto the sensor.

    Bookmark   March 10, 2011 at 7:15PM
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ionized_gw

Thanks for the explanation. This is one case where the name of a device corresponds pretty well with its function, but one can never be sure.

One more question if someone will indulge me. When did such safety devices become common in residential heating devices?

    Bookmark   March 13, 2011 at 12:06PM
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brickeyee

"When did such safety devices become common in residential heating devices?"

They have been added to gas 'boilers' for at least 20 years now.

Many if the units have no real bottom (thin sheet metal if anything) just a bunch of burner tubes with the gas jets and air dampers at the front and the burner tubes extending back.

The front is often open for air flow to the burner tubes, making it necessary to make sure the flame does not come out forward if anything goes wrong.

    Bookmark   March 13, 2011 at 4:24PM
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