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heat not working

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SAWYER

Lifer
I have central heat and air and a gas furnace in my attic. Yesterday I noticed cool air was blowing out of my vents. I went up in the attic and noticed the furnace was on, just no heat. The warning label on the side said it doesn't have a pilot light but uses an electric ignition and had a procedure to do it. I just shut my thermostat to off and have not messed with it, any suggestions before I call a heat and air guy to come look?
 
Well, the way my furnace works is like this:

1) Thermostat signals the furnace to start.
2) The induction motor starts (pushing air towards the jets)
3) The ignitor starts to warm up and glows a bright orange color
4) Jets kick on and blow gas over the ignitor (total of 4 jets, ignitor is on the right most jet)
5) The furnace fan kicks on to start blowing the warm air throughout the house.
6) The flame sensor (on the left most jet) detects whether there is a flame, if no flame is detected the furnace shuts off to avoid letting gas fill your house.

So depending on what step your furnace is getting to it could be a simple fix you could DIY if you're handy, or you'll need to call a pro.

I've replaced the induction motor, ignitor and flame sensor between the furnaces at my current and previous house.
 
On the assumption that you are getting gas to the unit (should be able to hear/smell it), the igniter is either dead and/or "clogged".

With the thermostat is on high; you should be able to hear/see the ignition activate.
No click/glow == dead

Clicking/glowing indicates that the thermostat is talking to the ignition system.
Serious issues then.
Otherwise best to replace ignition part then.

You can do it is a good DIY or pay the service call and small $$ for the part.

If you call for help; provide the furnace model number
 
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When I get home I will take a picture of the furnace and I will be by it and have someone turn on the thermostat
 
My Trane furnace has blinking light codes (on the main circuit board), when something is wrong.
I've replaced the board myself when it went bad. Total cost was about $90 after finding one on ebay. I'm sure a service call and board replacement would have been much higher.

Bottom Line: I love DIY projects as long as I have Google to turn to.
 
MixMasterTang said:
Well, the way my furnace works is like this:

1) Thermostat signals the furnace to start.
2) The induction motor starts (pushing air towards the jets)
3) The ignitor starts to warm up and glows a bright orange color
4) Jets kick on and blow gas over the ignitor (total of 4 jets, ignitor is on the right most jet)
5) The furnace fan kicks on to start blowing the warm air throughout the house.
6) The flame sensor (on the left most jet) detects whether there is a flame, if no flame is detected the furnace shuts off to avoid letting gas fill your house.

So depending on what step your furnace is getting to it could be a simple fix you could DIY if you're handy, or you'll need to call a pro.

I've replaced the induction motor, ignitor and flame sensor between the furnaces at my current and previous house.
Click to expand...
You might be missing the gas vent fan that has to run before the ignition if you have a high efficiency furnace with the PVC vent pipes going out of the side of the house.
 
SAWYER said:
I have central heat and air and a gas furnace in my attic. Yesterday I noticed cool air was blowing out of my vents. I went up in the attic and noticed the furnace was on, just no heat. The warning label on the side said it doesn't have a pilot light but uses an electric ignition and had a procedure to do it. I just shut my thermostat to off and have not messed with it, any suggestions before I call a heat and air guy to come look?
Click to expand...

Do you happen to have a dual-fuel heat pump / gas furnace?

The heat pump is basically your AC compressor running in reverse. Occasionally it needs a "defrost" cycle..(A/C mode) and will feel like cold air from the vents for a few minutes.
 
Call your gas utility company. Here where I live they will come out for free and inspect any gas appliances. If they can't fix it I'm sure they can point you in the right direction or give you an idea how to fix it yourself
 
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