I have a Rheem Criterion II furnace. I was trying to install a NEST thermostat and it didn't detect power. I traced the R wire back to the furnace, and the power LED is not on (and of course no 24v from R to C). The outlet the furnace is plugged into has 120v. I bypassed the door switch wiring, to see if the switch was the issue per someone's troubleshooting suggestions on this site, and still no luck. I was also looking for a possibly blown fuse, but there isn't one on the board. Does anyone have any suggestions on the issue or remedy?

My board is 1012-920A.

 

always always turn power off to replace anything to prevent future issues such as this. There may be an inline fuse some where on the low voltage wiring. maybe the transformer has a black reset-able fuse built in. if that checks out, grab a volt meter and check that you have 24v coming out of the transformer. if you still have trouble, let us know. hope this helps