Hi. I have a gas furnace, not sure of the brand. It is blowing cold air. When I watched it go 'on' before, here's how it generally works - the pilot light ignites, then generally several seconds later the furnace 'catches', makes a low rumble and starts sending warmer air through the vents.

Right now the pilot light ignites but the furnace catch (the rumbling sound) doesn't happen. At that time it starts blowing out air... cold air.

This has happened a few times... last year... but only when it was windy/raining... as it has been the last few days here.

I've tried turning the off switch and turning off the thermostat then restarting the thermostat and flipping the on swithch of the furnace. Still cold air.

The furnace is upright, in a closet, with a vent pipe going through the roof. That's about as technical as I get. Do you think the wind/rain is keeping the furnace from 'catching' ?

Usually the blower is brought on by a time delay, that is why it will blow cold air if the burner does not lite, you may have a corroded flame sensor (a rod with a wire attached and sticks into the flame) or a dirty burner, may also be that the pilot is not igniting.
The ignition control modual is very sensitive to moisture if you have a package unit, this may also be the cause, Good luck, Mike

Mike
Thanks so much for taking the time to respond.
Well the pilot is igniting, I see the blue flame. But I bet you are right about the sensor or the burner.
Of course it's a weekend.. when else do things go out! I'm going to have a service person in during the week to look at it.
I've read that the sensor can be easy to clean or replace myself but that sounds explosive :)



Usually the blower is brought on by a time delay, that is why it will blow cold air if the burner does not lite, you may have a corroded flame sensor (a rod with a wire attached and sticks into the flame) or a dirty burner, may also be that the pilot is not igniting.
The ignition control modual is very sensitive to moisture if you have a package unit, this may also be the cause, Good luck, Mike

If we can get a brand of furnace and model it will be easer to help. Remove the top door on the furnace a brand and model number should be on the side of furnace or bottom shelf of the unit.

Well, I tried the furnace this morning, the pilot light ignited and then out of the blue the burner or coil or whatever caught, there was the familiar rumbling sound and it worked.. started blowing out warm air.

The only thing that's changed is that we aren't having a steady downpour of rain. Do you still think it's worth having the service person check the burner or could it possibly be rain related?

I'm still trying to find the furnace brand/model number... it's not on the front where it should be.

I would have it checked over by a professional unless you want to get caught with your pants down at 10 degrees. It can get real cold real fast when the furnace does not work.

I have a similar problem as you. It seems my sensor is slipping down just a bit due to the outside casing (ceramic maybe?) being cracked. I cleaned it, but it still seems spuradic.

After the pilot lights, if I blow on the pilot flame then the furnace lights up just fine. I figure it's blowing the pilot flame more onto the sensor.

Does this make sense?

Also, is the "sensor" the same as the "thermocoupler"?

My ignitor heats up for about 10 sec and then it goes out but there is no flame from the flamer. It runs for about 10min. Blowing cool air and then it goes out

Furnaces work or do not work. As I mentioned I would not want to get caught with a furnace that has problems when it gets cold. Everyone waits till its cold to get the furnace fixed then when the repair man cannot make it for a few days because they are busy the customer freezes. Something caused the unit not to work.

Sensor is not the same as thermocuple.
Cracked ceramic part should be replaced. It is in the ceramic for a reason. The ceramic acts as a insulator.

renard start a new thread so we can keep these problems separate.

''Also, is the "sensor" the same as the "thermocoupler"?''

Flame sensors are a newer technology that replaces the thermocouple. You can find pictures of each at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html