# Furnace will not start when extreme cold



## ColdandConfused

Crazy problem I can not figure out for years. 

My furnace(Gas, forced hot air) has an out and intake pipe going outside.

It works 99.9% of the time.  However, at night in extreme cold weather it will not work, it will work.  Funny thing, my furnace will not work if it is too cold. 
I have read many of the post, however, they just don't fix my issue.  I have had many people work on this issue with me and some professionals and the problem persist.

We have changed the inducer motor, the flame sensor, the fuse, the batteries in the thermostat.  

This has been going on for years, since it was put in I beleive.  

Very cold night, it will not work.  About 11am even a very cold day, it just starts working.

I think it is the cold air in some way, however, I can not get anyone else to beleive me, more important, I don't know how to fix it even if it is the cold air.

Any one that can help, It would be such a blessing.

Thank you in advance for your help.

Cold and Confused


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## JohnchambersJr

I have not looked at any of the previous reply postings.  I just happened to notice this tonight.  I don't know what cold is but I would look at you safety cicuits that insure certain things happen before other things can.  There are vacumn and pressure systems that insure that it is safe for your furnace to fire.  The control circuits generally have red wiring to them.  The vacumn and pressure ports that activate them might be where the problem lies.  The cold may be causing condensation which could block them.  The ignitor, inducer motor etc. are very unlikely.  Not knowing the furnace and it's age make this diagnosis difficult.  If you are in snow country could snow block a vent?  Is the furnace in a heated space?  Does it have an electronic control module?  Are there and vacumn/pressure lines that have accumulated water?  Hope this helps. John


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## paul52446m

ColdandConfused said:


> Crazy problem I can not figure out for years.
> 
> My furnace(Gas, forced hot air) has an out and intake pipe going outside.
> 
> It works 99.9% of the time.  However, at night in extreme cold weather it will not work, it will work.  Funny thing, my furnace will not work if it is too cold.
> I have read many of the post, however, they just don't fix my issue.  I have had many people work on this issue with me and some professionals and the problem persist.
> 
> We have changed the inducer motor, the flame sensor, the fuse, the batteries in the thermostat.
> 
> This has been going on for years, since it was put in I beleive.
> 
> Very cold night, it will not work.  About 11am even a very cold day, it just starts working.
> 
> I think it is the cold air in some way, however, I can not get anyone else to beleive me, more important, I don't know how to fix it even if it is the cold air.
> 
> Any one that can help, It would be such a blessing.
> 
> Thank you in advance for your help.
> 
> Cold and Confused



On the out side of the house does your intake and exhaust  go up through the roof or out the side wall. If through the roof does the intake have double ells on it. If the intake is side wall does it elbow down? Do you turn your heat down at night? .  The reason i am asking these questions is, i am
 wondering if you are getting a gravity flow down into the burner chamber.
 All gas valves are made to operate at a certain ambient temp, so if your valve gets too cold it will not want to open. Like on out door unit we have to use cold ambient gas valves.  Paul
 Can you show me a pic. of your out side pipes?


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## billmarti

I have had the exact same problem.  I occasionally get lucky and get the furnace started by placing my hand over the intake outside which seems to cause a motor to rev up higher than it otherwise would and then the furnace starts.  I think the problem is related to air density and chamber pressure differentials which control the burner ignitor.  By placing my hand over the intake when the furnace is trying to start, it changes pressure differentials and the furnace finally starts.  I have talked to many service people to no avail.  Nobody seems to recognize my solution, but it has saved my marriage.


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## Wuzzat?

billmarti said:


> I have had the exact same problem.  I occasionally get lucky and get the furnace started by placing my hand over the intake outside which seems to cause a motor to rev up higher than it otherwise would and then the furnace starts.  I think the problem is related to air density and chamber pressure differentials which control the burner ignitor.  By placing my hand over the intake when the furnace is trying to start, it changes pressure differentials and the furnace finally starts.  I have talked to many service people to no avail.  Nobody seems to recognize my solution, but it has saved my marriage.


The service techs should be able to come up with measurements that may say why your method works.  It's called hypothesis testing, and confirming or disproving your fix will benefit them if they come up against this in the future.


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## Blue Jay

We had a similar problem with my Mom's mobile home, we put a trouble light with a 75W bulb in next to the inducer motor and when it was going to get into the teens she would just plug it in. Never had a problem with it after that.


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## Wuzzat?

Blue Jay said:


> We had a similar problem with my Mom's mobile home, we put a trouble light with a 75W bulb in next to the inducer motor and when it was going to get into the teens she would just plug it in. Never had a problem with it after that.



How did you know to do that?


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## nealtw

Common sence applied by a handyman, if it only happens when it's cold, keep it warm.


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## Wuzzat?

I think now 1.5 oz of 80 proof rum impairs my cognitive (and motor) functions.
Another duh' award for me.


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## Blue Jay

Wuzzat? said:


> How did you know to do that?



Since it only happened when very cold outside and the fresh air intake was right below the motor, only made sense to keep it warm. Had used the same idea for several years to keep the pressure tank and piping from freezing that was in a shead outside, 2 light bulbs on a thermostat.


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## rogerknapp

I suspect your venting or cumbustion air go outside and check your venting or intake for obstructions including screens which may frost over or ice building up . if that checks out try temporarily removing your combustion air intake pipe and see if it improves that would tell you if your problem is in that pvc pipe .Or it could also be a weak pressure switch or a leak in the tube to it.


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## Miztreese1

paul52446m said:


> On the out side of the house does your intake and exhaust  go up through the roof or out the side wall. If through the roof does the intake have double ells on it. If the intake is side wall does it elbow down? Do you turn your heat down at night? .  The reason i am asking these questions is, i am
> wondering if you are getting a gravity flow down into the burner chamber.
> All gas valves are made to operate at a certain ambient temp, so if your valve gets too cold it will not want to open. Like on out door unit we have to use cold ambient gas valves.  Paul
> Can you show me a pic. of your out side pipes?


Paul. Can u say life saver!! I have my exhaust pipe on the side of my house. So I bundled up and went outside TO check it because my heat wouldn't work.  And low and behold it was blocked with snow. I cleaned it out. Went back in and reset my furnace.  And it clicked right in. Thanks so much to your response from an earlier post. U saved me andy girls. We were freezing!!! Bless u


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## Wuzzat?

Wouldn't an exhaust pipe melt snow?


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