Trumpy,
Excellent job on the design! One comment - many boilers in the states are required to have a separate line voltage series of safety switches for over pressure, over temperature etc. which remove operating power to the fuel supply and blower and activate an input to the controller. (Very similar to centrifugal chiller safety circuits). These safety devices or limit switches are only manually resettable. The idea is that if the controller fails, a serious event is avoided.
You have obviously given this project a lot of thought and work. Congratulations!
Homer
