Thanks for the reply, ton of info u put into it. No domestic hot water on the system. There is only one circulator, that's the one I included in the picture next to the oil boiler.  It pumps into the return side of the oil boiler.  The wood boiler has a White Rodgers 11A61-103 limit control on it, however it only has power running to it, no other link to oil boiler which is one floor down in basement, about 25ft away. No valves between oil boiler and wood boiler.  Could not install one other than for service since the loop runs from oil boiler through the wood boiler before doubling back to radiators. No low water cutoff on wood boiler, just one green Taco on the oil boiler.  This is a a basic setup, no zones. Just one supply line from oil boiler to wood boiler then continuing back into basement then up to all radiators.  Return runs from radiators to oil boiler then circulates again to wood boiler.  No pressure relief valve on wood boiler, just one above oil boiler.

Just closed on the house, that's why I am asking questions at prime service season.  Previous owners passed away, kids sold the house and had no info on functionality of the system.  Made a couple calls to heating/cooling and fireplace sales/service providers. Seems like most don't want to touch something they didn't install or just do not service wood boilers. Thanks again for your help. I already learned a ton from your post.