I have a Rheem Criterion II gas furnace. It has been working this winter and went out this morning. The unit cycles, but the gas only stays lit for 7 secs. goes out, lights again for 7 secs. goes out, and then the blower turns on. I tried this with the thermostat turned to on as opposed to auto, with the same results. The green leds are solid, the amber led never lights. I replaced the flame sensor, with no change. I assume the polarity doesn't need to be switched, since it's been working. HELP!

The furnace does not recognize the exhaust vent blowers operation an automatically shuts down. Check the exhaust vent blower switch operation.

The furnace does not recognize the exhaust vent blowers operation and automatically shuts down. Check the exhaust vent blower switch operation.

The furnace does not recognize the exhaust vent blowers operation and automatically shuts down. Check the exhaust vent blower switch operation.

The exhaust blower is the first thing that comes on.

Now I noticed that the amber light blinks once when the unit fires up the first time, only to shut back down after 7 seconds. I looked at the safety switch and noticed the tech bypassed it when he was out here last month... he told me the furnace wouldn't lite then because of a loose wire. I guess the switch was bad and he just bypassed it instead of replacing it. Anyway, the black to black connections inside the box where he bypassed the switch are good, so are the white to white and green to green

Does it have a flame senser,, if so it could be that it needs cleaning,, remove and polish real good with very fine sandpaper or steelwool,,

I installed a new flame sensor right before I started this thread. This is really stumping me! Btw... the blower won't come on when I turn the thermostat to on from auto, but it does come on after the second time trying to light.

On mine I was having the same problem and found the tube that goes to the exhaust blower sensor was stopped up with crud, might check that.

Thank you for your answer. It solved my problem

WMProop. Thanks for the answer it solved my issue