Hi to everyone on hearth.com, I am new to the forum as well as new to a PB105 boiler. I just purchased this boiler with the plan of installing it in series with my current oil boiler system. I have searched a lot around about series and parallel but I just seem to think that series may be easier. I am in no way certain that is the way I am heading but I would like other peoples opinions on it. Also I was wondering if I needed to add another circulator pump on the new system. My current is controlled with three zones on zone valves with one circulator. My plan was return of zones into return on PB then supply to return on OB then supply to zones but I am not sure if I need to be able to circulate through both boilers when water is being heated with no call from zones. Any input would be appreciated.