[rohrmann]

I think you will need to pull the water heater out, at least far enough to access the box where the relay is located. You will probably need to disconnect the propane line, but if you don’t have to completely remove it, you might be able to leave the water lines connected. When I replaced our water heater in 2016, I was able to do the swap in a couple hours, and that included transferring the relay box from the old unit to the new one. There are some screws that need to be removed and the caulking at the flange where it attaches to the outside wall needs to be cut to allow the unit to be pulled out. You will also need to cut the caulking around the propane line.