I have an oil boiler for heat. 14-3 cable runs from the panel to a thermal cutoff above the boiler, then into the boiler's control box, and from there to a Taco controller that manages three zone thermostats and controllers for forced hot water heat.
At the panel, the 14-3 cable is presently double-tapped so that both the black and the red are attached to the same 15-amp breaker.
I'm in the process of migrating the whole circuit to a subpanel so I can put the boiler on a transfer switch to a generator for backup power. I'm tempted to attach the red and black wires to 2 ganged 15-amp breakers, but I'm afraid because I don't understand the original intent of this wiring.