I have a rheem classic quiet 80 . furnace starts up but the igniter will not kick in to start the flame

Fix Furnace Flame Sensor (Flame That Goes Off) - YouTube

? 1:22
https://www.youtube.com/watch?v=fBJ3r9MUa-U
Nov 29, 2011 - Uploaded by RochNoure
A Furnace Flame Sensor is a safety device that reads the temperature and ... easy fix, but the furnace is ...

Troubleshoot the ignitor of the Rheem RGDA model gas ...

? 5:53
https://www.youtube.com/watch?v=Bx1pXONg2Oc
Dec 12, 2012 - Uploaded by grayfurnaceman
Troubleshoot the ignitor of the Rheem RGDA model gas furnace.... Jun Sim 5 months ago ... My lennox ...Missing: lx2000

Rheem Criterion II No Heat - YouTube

? 0:47
https://www.youtube.com/watch?v=yOSk6qvpWbA
Jan 7, 2010 - Uploaded by Work12Progress
Rheem Criterion II gas furnace model # RGPH-07EAMGR. When a call for heat is made t wo green led's ...Missing: lx2000

Heater will not kick on unless... [Archive] - Self Help Forums

www.selfhelpforums.com/archive/index.php/t-2153.html

Oct 19, 2004 - 25 posts - ‎9 authors
After a certain amount of time of not running, the heater will refuse to kick back on. ... 2 flashes, then a 2 second pause = pressure switch is open. What do .... On LP gas furnaces, the spark starts and the gas valve opens. ... Buffing them up with a little steel wool (5 minute job) is a good annual PM thing to do.

Not sure but its possible your thermo coupler is shot and needs replacing. If you have a pilot light it could be out but the furnace should not start if the pilot is out as there should be no oower getting to the controls unless the pilot is trying to let it start. A bad thermocoupler will not let the flame start.

in front

Hello, check the flame sensor, this is a metal rod on the opposite side of the igniter. Turn off power to the furnace remove flame sensor and clean it up with some steel wool, then reinstall and turn power back on to the furnace.

Probably the flame sensor is dirty. Should be wire protruding into flames opposite end of flame tubes from igniter. Clean with steel wool.

Open the two side panels. The filter is at the bottom held down with a wire spring. Release the spring and the filter can be removed.

Bad fan switch. It may also be called a fan limit switch. If your furnace is less than 5 years old, the switch is part of the circuit board and you will need to replace the board.

Sounds like it could be a dirty or bad flame sensor.
When the burner lights ,there is a flame sensor in the flame and it is suppose to sense the flame and send a signal back to the control board which will keep the gas valve open, if it gets dirty or is bad it doesn't send the signal back to the board and the board will shut the gas valve off and after three tries it will lock out the furnace and you have to reset it to get it to work again.
The flame sensor looks like a wire and it's in the flame usually it will get gas deposits on it, then it won't work.
You can clean this sensor with an extra fine piece of steel wool, but before you attempt to do this DISCONNECT ALL POWER TO THE FURNACE.

I have this same POS model. It is not the thermostat. this model is just garbage and cant wait to get something that works right. i have been fighting this thing for 4+ years now.

I have a Rheem Classic 80 furnace that would ignite but not stay lit. Cleaned the ignition sensor which was easy to get to and the flame sensor which was under the burner plate and it fired up and stayed lit. The flame sensor was about 6" under the burner plate. Easy to get out, but tough to get back in. Used the old piece of paper shim trick to get the screw to "stick" in the socket and it was much easier to position the screw and get it back where it belonged.