Welcome! Here are the website rules, as well as some tips for using this forum.
Recently a contractor pointed out that my furnace has no backflow preventer. Oil company says it only recently became a required component, and they installed my furnace before the code changed. I am looking to see what else they might not have installed. We have radiators, and it's my understanding that the system needs an air separator.
What I see immediately before the air expansion tank is something called a microbubble resorber-- is this the air separator?