You actually did throw the switch to turn on the heater and not just turn on the propane valve at the tank, right? Just checking.
I'm sure that there must be a remote, easily accessible switch on the van interior. Every one of my rigs had one. Your Tellero manual should tell you where this is. Do you have a Firefly? Near it? On the side of a cabinet?I have a Truma its under the side bed its all sealed only a small door to it i looked in there and could not see any switch but the manual shows it has a switch on the truma unit it self