I also had that issue, not during a boil, but overnight. The remedy was to just close the ball valve between the raised flue pan and the syrup pan. Fortunately mine never went on the floor, I had my syrup pan made 4" taller than a typical syrup pan (Also had 4" taller flue pan too). Before I started closing the ball valves (I have two, same side reversible) I did get greeted with a flooded syrup pan a few times, but it was about 5" down from the top. I didn't pump the excess back into the flue pan, I just opened the feed line to the flue pan, once the flue pan was at 1/4" above the flues I lit the fire. It took a while to get down to 1" in the syrup pan, but it worked. I'm not saying this is the best way, it's just how I did it. I could have rather easily pumped it back into the flue pan, I just didn't.
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.