Does the blower fan on the furnace run and it just won't ignite or does nothing happen?
The steps could be several things. The first place to start is checking fuses. It could also be a connector loose, a bad switch or something mechanical. There may be an inline fuse that protects them.
I had the same problem with our previous coach. After confriming the fuse was ok, I pulled the switch plate off and found where the switch wiring harness plugged into another wiring harness one of the two locking tabs were broken off letting them partially separate. Simple fix was a zip tie around them to make sure it didn't vibrate loose.