Refired my boiler today.
I've been doing some upgrades. Repiped the supply and retturn fron the outside coal boiler into the oil fired boiler. Did a nifty hookup called " The ala Sting" The Closely spaced tee stuff. Notice the supply and retun to the boiler
See where I cut a Tee into the return and hooked the other end into the flow check. With this arrangement there is no heat loss from the oil boiler. While it isn't an automatic system I'm able to keep boiler temp low, turn the power off to the oil burner with the switch on the wall.
I have a relay that is fired by the domestic water circ pump that initiates the t-t contact on the controler and an outside t-stat set at 50 degrees in parallel with that so when the temps are low the circ pumps run constantly. I decided to isolate the oil boiler after placing my hand in the barometric damper and feeling all this heat running out the pipe. My wife can turn two valves and flip a switch and be back in business if I'm not around. Not the simplest but also not the most complicated. Ala' Sting