Woke up to temperature below where it was set, furnace not turning on.

Reset circuit and it turned on, blew cold air for about 90 seconds and turned off.

Replaced thermostat, reset circuit, same thing happened.

Opened furnace, removed flame sensor, sanded it lightly, replaced it, turned back on furnace, same thing happened.

Here's what happens when thermostat is set at higher temperature than house and I turn on and off switch at furnace
- blower goes for about 90 seconds, get error code 12
- ignitor glows red but burners do not ignite
- ignitor turns off and tries again another two times, get error code 34

Also tried pressing the reset button between two wires but that did not help
And, tried tapping gas valve when coil was red but that did not help

Inside your air handler fan housing should be a chart with the flash codes. Typically they will be pressure switch not closing, flame sensor or high temp limit, sometimes rollout. Yours sounds like either of the first 2. 34 is probably a lockout code. If you Google" Carrier 8000 codes" you will also find them.

thank you, code 34 is Ignition Proving Failure
It says that the control will try 3x (which it does) before Ignition Lockout which I guess means is a safety and it turns off until I reset it
It says
- flame sensor must not be grounded
- oxide buildup
- proper flame sense microamps
- gas valve defective or turned off (valve is on and gas works on my stove and hot water heater)
- defective hot surface ignitor
- low inlet gas pressure
- inadequate flame carryover or rough ignition
- green/yellow wire must be connected to furnace sheet metal

thank you, code 34 is Ignition Proving Failure
It says that the control will try 3x (which it does) before Ignition Lockout which I guess means is a safety and it turns off until I reset it
It says
- flame sensor must not be grounded
- oxide buildup
- proper flame sense microamps
- gas valve defective or turned off (valve is on and gas works on my stove and hot water heater)
- defective hot surface ignitor
- low inlet gas pressure
- inadequate flame carryover or rough ignition
- green/yellow wire must be connected to furnace sheet metal

What's my best next step? Replace hot surface ignitor?

- gas valve defective or turned off (valve is on and gas works on my stove and hot water heater)

Please review all the videos in these links.

https://www.youtube.com/watch?v=I86joWL66aE

https://www.youtube.com/watch?v=iDnkdKsZhc0

There are more links to the right. Let me know if they help any.

Thank you, I've watched the videos and find them helpful but still have not solved problem

My ignitor glows orange, I hear a click but the burners do not light
My burners appear to be in good shape and I do not smell any gas
My gas and gas valve are on so not sure why gas does not appear to be flowing to the furnace

What is error code 12? "gas valve are on so..." How do you know the gas valve is working?

Error code 12 had to do with blower

I didn't know if gas valve was working and read that if I tap it with a screwdriver while the ignitor is orange that burners might light, but it didn't
I read someplace else that I should tap the pressure control switch with a screwdriver instead. I just did that, and it worked! I heated the house and then it turned off. I then turned up the thermostat and this time the burners came on without me tapping.
Hopefully, problem solved but will monitor

Thanks for the help

<br>
It worked for about 12 hours and then didn't light again.<br>
I reset it and tapped the pressure control switch when the ignitor was orange and it lit again but obviously something is bad<br>
Does the pressure control switch go bad or is it a sign of a bad board or something else? The board was replaced once about ten years ago

47279

By the way, the part I refer to as the pressure control switch is the rectangular black box next to the gas valve. Is that the right name for it?

47279

By the way, the part I refer to as the pressure control switch is the rectangular black box next to the gas valve. Is that the right name for it?

The attachment is not working.

Thank you, here's a link to the pic, seems to be a site problem

http://postimg.org/image/qwmpn3e29/

I didn't open the link but it will have a flex tube into the inducer fan case and 2 or more wires. Remove the flex tube and carefully try to clean the orifices with a wire. Start at the inducer as that is typically where dirt will build up. They are inexpensive to replace, $20 or so.

Thanks for the suggestion but I must have described the part poorly as there is no flex tube attached to this rectangular black box.
It is located close to the gas valve and has a three wires that attach to it at two different places (two wires at one contact, one wire at the other).
Those wires are the only items connected to this part

The link you provided gives your personal info, and some nice pictures of scenery, but NO part.

The link you provided gives your personal info, and some nice pictures of scenery, but NO part.

Ugh - tried again -
View image: carrier furnace (http://postimg.org/image/qwmpn3e29/)

Obviously that is the inducer fan in front, the black flat unit below is your high limit safety. Don't know what the arrow is pointing to, could be a pressure switch but I have never seen one directly on the gas valve. I believe the pressure switch is the device next to the inducer fan, has a yellow tag on it. Is this a 2 stage heater?

Here's a picture of the part and the area it is in from above - you can see the gas valve on the bottom right and then just above it and to the left is the black piece that I'm referring to with the wires unplugged.

http://postimg.org/image/f88tj8og9/

I don't know if it is a two stage heater

Here's a better picture with the tip of the screwdriver touching the part that I need to tap to get the burners to light

View image: carrier furnace part with screwdriver (http://postimg.org/image/sry73tznp/)

That is a solenoid, probably for the gas valve. The contacts are corroded or possible dirt in the solenoid slug that keeps it from retracting. Google the gas valve model, it should tell you for sure.