I want to flush out the system on my CH but as its a combi boiler system I'm not sure how to do it? I'm not looking to power flush it, just add some sludge eater for a week or so and then flush it and add fresh inhibitor etc. So do I just undo the system drain and turn on the filling loop and flush it out like that? Or is the a jumper on the PCB that turns the pump on? Boiler is a Alpha 240 eco.