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Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 2014
Experience:  14 years experience in the HVAC field of service, installation, Manual J & D calculations
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Why does my gas furnace shut down when its very cold?

Customer Question

why does my gas furnace shut down when its very cold or very windy out . i have to reset and it will come back on . when i look into little window it looks like something is blowing the flame out and then it goes out. is the air to cold . i dont get it its a two year old house
Submitted: 6 years ago.
Category: HVAC
Expert:  Matthew replied 6 years ago.
Is this a 90% furnace? You should be able to tell by the type of vent pipe coming off the furnace is it PVC or metal?
Customer: replied 6 years ago.

i think it is a 90% furnace its pvc pipe

Expert:  Matthew replied 6 years ago.

Then the wind is pushing against your vent going out of the house. there should be a 90 degree elbow on it where comes out of the house. If there isn't then the wind is pushing right into the pipe. I will post my 90% explanation so you better understand what is happening. A 90% furnace condenses the exhaust gas so it has to drain this water out of the venting system. Every now and then on a 90% furnace if the vent pipe has a dip and traps this water it allows it to be hit by cold air when the furnace isn't on and will freeze. When it is frozen in the pipe it will block the amount of exhaust you are getting and not allow the pressure switch to prove therefore not turning on the igniter and causing a fault in the system. The system will go into a lockout time of 1 hour normally and then try again or you have to reset the thermostat or power to get it to try again. Another thing that can happen in extreme cold climates is if the drain going to the outside of the house gets plugged up or again freezes because it is not insulated at the outside or has traps caused by dips in the line then it will back up the water into the combustion chamber and cause the same type of havoc. I have even run across some exhaust vent pipes that have a dead family of birds in it or a bees nest.

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Customer: replied 6 years ago.
there are two lines coming out of my house the one thats taking in air has 90% the one thats blowing outr air does not could the wind be blowing into the output and blowing out the flame or does the in put need to be extended so the wind doesnt blow in.the furnaced will come on but it looks like its been blown out
Expert:  Matthew replied 6 years ago.
The pvc pipe that is hooked to the inducer motor is pushing air out, the one that is hooked to the side of that is just a open vent that allows fresh air into the furnace cabinet this is what makes it a +92% furnace. This one should be open at the outside does not need an elbow on it. It could be your flame sensor or your high limit that is making the furnace go off. When the flame goes off does the blower motor keep on running? When it goes off it should give you a blink code on the furnace control board see if you can catch that blink code when it fails.
Customer: replied 6 years ago.

i put a 90% elbo on pipe today that blows air out it seems to have worked . before that i stood outside next to pipe and when the wind blew i could hear my furnace begin to sputter . it only happends when its very cold and windy out .when its above freezing the furnace works great do you think i solved problem with the 90% and i put a 10inch extension on both pipes . its been about 9hrs and i have no problem its been cold and windy all day .let me know if you think i may have solved the problem.

Expert:  Matthew replied 6 years ago.
Yeah, I believe you may have. just keep an eye on it.

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