Steeping grains? Partial Mash or All Extract? What volume of water are you heating? If your indoor stove is capable of boiling those volumes go for that. If you are relegated to cooking it up on a burner, try heating the water to where you want/need it then adding steeping grains, cover, remove from burner and can wrap in an old winter coat or comforter. You will get minimal temperature drop and should be fine.
Another thing to try would be to raise your pot a little off the burner so that heat vents better. Also, using a binder clip and a paint strainer bag (Home Despot has them for a couple bucks) to keep it elevated off the bottom will help too.
Most burners should be able to have the pressure reduced to just the barest flicker of flame above the burner. I have a KAB burner and can get it down to almost the point of going out just from the dial on the regulator (high pressure)