Turn the circ function off then or at least program to only run when needed.
Hot water recirc by many could be considered a luxury, and it comes at a cost to keep that loop hot.
Its not the heaters, but what you created is a constant heating loop all the way to the farthest point and then back. Depending on whether or not the supply and return pipes are insulated and how well only makes it worse.
Putting a tank back in and still using recirc would be even worse energy costs. The difference in operating efficiency is about 15% so put the tanks in and use recirc and be prepared to buy even more propane.
(Guys: note I said 10-15% versus using 30-40% which is commonly quoted. Remember the return temps are coming back elevated to be reheated, thus the unit is out of condensing mode and cycling besides, but without standby/flue loss calculated)