Furnace just quit working?

[TMfor4ofus]

We just came back from a two night stay. Furnace was working fine until this am. It was cold so I wanted to run it for a bit. The fan runs and just blows cold air. Tried restarting it several times pulled the panel and checked all elec connections. Checked fuses? The stove and fridge work fine. Got good power and gas? Any ideas? Its a 2011 2720 electronic auto light?

[Bill]

If the fan is running, it is not an electrical problem.

The furnace won't light until it knows that there is enough air blowing through it to keep it from overheating. The fan blows the air, and the flow of air is sensed by a device called the "sail switch" - the air flow pushes the flat sheet metal sail. Until the sail switch says "air flow is good", the flame won't start.

The sail switch can fail to move either because there is truly not enough air, or because the movement of the sail is blocked by accumulated dust. Since the furnace is near the floor, this can easily happen.

A similar problem can occur if the vent to the outside is blocked. Check for bugs, webs, mud in the passage through the wall to the outside.

Take a look in your furnace user's manual - it will give you the details.

Bill

[TMfor4ofus]

If the fan is running, it is not an electrical problem.

The furnace won't light until it knows that there is enough air blowing through it to keep it from overheating. The fan blows the air, and the flow of air is sensed by a device called the "sail switch" - the air flow pushes the flat sheet metal sail. Until the sail switch says "air flow is good", the flame won't start.

The sail switch can fail to move either because there is truly not enough air, or because the movement of the sail is blocked by accumulated dust. Since the furnace is near the floor, this can easily happen.

A similar problem can occur if the vent to the outside is blocked. Check for bugs, webs, mud in the passage through the wall to the outside.

Take a look in your furnace user's manual - it will give you the details.

Bill
The fan blows hard, just cold air. I checked the owners manual for furnace. Doesn't say much except operation how to and lots of details of installing. I just lit the water heater, fridge, and oven no problem. Still only cold air from the furnace? Arrggg. Thanks though.

[tentcamper]

once the sail switch send the single the air is moving through the furnace and out the exhaust it will try to light.

There is a small window into the fire box. With you face laying on the floor look through it to see if it tries to lite. Can not remember if it's a spark or glow. You might need to take off the front cover under the seat to see through it. It will try to lite somewhere between 15 sec and 2 minutes after the fan starts.

If you see a spark or glow. The sail switch signal was sent and gas flow is not correct. No glow or spark? Either sail switch signal not received or the igniter is not working.

Let us know what you see?

PS: I think it has limited numbers of times it will try to lite. I think it's 3, but I believe the fan will just keep running. After it times out, you must turn off the furnace to reset it for it to try to lite again.

[TMfor4ofus]

It's working! Yea. except I'm not 100%sure what it was. I was checking the ON/OFF switch and it seemed kinda flaky. When it went to off it barely came away from the terminal so I tweaked it so it makes a better gap when off?? IDK but after that it fired up after about 15sec after the fan came on. I heard a click and poof flame in the burner. As I said I'm not sure because if the ON/OFF sw in the therm just starts the fan then that wasn't it because it always started the fan. Anyhow it works now. I did it about 3 more times and it lit each time so I'm happy and at least I know what to look for and listen for now. :o Thanks guys it will be tested in two weeks. Wont be critical because we will be plugged in and running space heaters.

[LoveToCamp]

You don't say if you have a digital thermostat, or a mechanical one. If digital, change the battery in the thermostat. My furnace did the same thing a few weeks ago, and it was due to a low thermostat battery.

[TMfor4ofus]

Its the old school mechanical type.

[tentcamper]

There is a minimum voltage the furnace needs for the control board. Maybe with that poor connection at the stat contacts, there was enough voltage for the fan but not for the other circuits?

[TMfor4ofus]

Maybe? I'll be testing it each time we set up for a while.