I'll just add a bit more: Possibly there's still air in the line and it hasn't purged out yet (from the propane refill). Have the wife turn off the switch, then you take one of those long-tipped flame lighters and stick it into the tunnel area by the water heater piezo lighter. Now have her turn on the switch and you fire up your lighter to see if anything's coming thru the gas tube.
If no gas, you gotta go to see if the regulator solenoid is getting power... If regulator solenoid is activating, then you've got one of those notorious little spider webs in the burner tube or orifice blocking the gas. If the solenoid is not opening to allow gas through, then it could be a bad brain (try cleaning the wire contacts with a pencil eraser). -Some brains had little blade fuses (3 or 5 amp, easily visible) that you could check. Try jumping out (bypassing) the thermal fuse once too.