Apologies if this has been answered previously. Various searches didn't turn up what I was looking for but I may not be using the correct terminology. I recently had a PB105 installed in series with my current oil boiler. These are the settings initially made by the installers: OAT: yes DHW: yes Feed Rate: 4 Igniter Mode: Auto PB105 Min: 165° PB105 Max: 175° Oil Min: 150° Oil Max: 160° Hot Water: 120° What I wanted to know is if there is a guideline for the min & max settings on the oil boiler that work best in concert with those on the PB105 - something that I've seen referred to as a "head start" in another thread. In other words, is there a recommended base difference between the Min setting on the PB105 and the max setting on the oil boiler in order to ensure I'm not blowing through oil needlessly? Example: 5°? 10°? 25°? I understand the oil boiler will run when calls for heat and hot water are made, which I want in order to exercise the unit. What I want to do is ensure that the oil boiler run time is minimal. Thanks in advance for any recommendations/suggestions!