I think I have it backwards. (I do that often) My machine is plumbed in, and the pump comes on to fill the boiler, even though I would expect that line pressure (generally) exceeds boiler pressure. It sounds like this is to use the tank as opposed to the line for fill. So, if I wanted to bypass the pump, I supposed I would do the same thing, in reverse, and THEN unplug the power to the pump. -Dan