# Solved: Gas furnace not igniting



## DIYGUY (May 10, 2011)

Model: Carrier gas furnace (home heating system)
It was working properly but yesterday stopped working. I read the instructions on label and tried to start it.
1-turned off the switch.
2-Set the thermostat to lowest level.
3-turned on the switch.
4-Set the thermostat on desired level.
Result: felt the smell of gas but no ignition.


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## Koot (Nov 25, 2007)

Determine whether the furnace has a pilot light or an electrically operated 'hot surface ignitor'. I'm guessing it has a hot surface ignitor. If so, that's probably your problem...and needs to be replaced, which is easily done in just a few minutes by most anyone. Hot surface ignitors are simply mounted and have a plug on the end of a short [wire] pigtail. They cost about $30-$40.

Just so you know how the hot surface ignitor works - when the thermostat calls for heat a signal (electricity) is sent to the ignitor, which heats up to a very high temperature. Then another signal (electricity) is sent to the natural gas valve, which opens and gas flows toward the ignitor and ignites the natural gas. If the hot surface ignitor has failed there is no gas ignition...and thus no fire in the furnace...and thus no heat in the house. The furnace has safeguard controls that prevents gas flow if the hot surface ignitor fails to ignite the gas...so you do not need to be concerned about any safety issue.


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## DIYGUY (May 10, 2011)

Thankyou for your prompt reply. I hope it'll solve the problem.


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## Koot (Nov 25, 2007)

DIYGUY said:


> Thankyou for your prompt reply. I hope it'll solve the problem.


Please let us know if that was the problem.


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## DIYGUY (May 10, 2011)

The problem was with the "Hot surface ignitor". I Replaced it and the furnace is working fine now. Bought new for CAD 38.00 .
Thankyou for your help.


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## Koot (Nov 25, 2007)

DIYGUY said:


> The problem was with the "Hot surface ignitor". I Replaced it and the furnace is working fine now. Bought new for CAD 38.00 .
> Thankyou for your help.


Excellent! :up: Glad we could help...and that it was an easy and cheap fix. 

Please mark your thread "Solved".


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## Drabdr (Nov 26, 2007)

Koot, thanks for that explanation. I haven't heard of those Hot Surface Ignitors before. I can't imagine they would get hot enough to ignite gas, but I guess they do. 

Anyway, I learned something new today. :up::up:


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## Koot (Nov 25, 2007)

Drabdr said:


> Koot, thanks for that explanation. I haven't heard of those Hot Surface Ignitors before. I can't imagine they would get hot enough to ignite gas, but I guess they do.
> 
> Anyway, I learned something new today. :up::up:


Yes, they do get very hot - very quickly. The hot surface ignitors use a thin silicon oxide (SiO2) layer that is formed on the surface of the ignitor which can reach temperatures approaching 1,000 degrees F in about 15 seconds.


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