A conventional propane canner can boil syrup. You must monitor the temp and regulate properly. Once you get to bottling temperature you need to shut the burner off and keep track of the temp. When the temp falls you relight the burner. When I had that type of canner I heated to 190 and shut it off. As it got down to 182-183 I relit it and ran it on low until 190 again. Anytime the temp is over 180 but not over 190 you can be bottling. If filling 1/2 gal or gal you will use the syrup up in one cycle generally, if filling small containers you may need to relight 1 or even more times depending on how small the containers you are filling.
On the other hand, I now use a 16 gal water jacketed canner, 240V element. I leave the thermostat set at 185-186 and turn it on or off by the circuit breaker. This canner takes syrup to the 185-186 temp and holds it there. You can hear the heating element cycle on and off as needed to maintain the temp, that's something my old propane fired canner could not do.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.