My water pump on my boiler is making noise. I was going to change it out. It is an American Standard with a Gossit pump. On the zone manifold there are drain valves. Before changing pump, I was going to shut off water supply to the boiler, then open up drain valves to relieve the pressure and then change out the pump. After installing the pump before I turn power back on to the pump, do I turn the water supply to the boiler and open the drain valves to let air out, or turn power on first, then open up the water and drain valves........thanks .......Karl