When my boiler reaches anything over 195°F my circ begins to cavitate really bad. I don't believe it's pulling air down into the supply because the port is 8-9" below the surface of the water. I've been told it's called "net pressure suction head", is that what I'm experiencing? What is the best way to alleviate the problem? Here's a picture of my supply port locations. I'm only using the one to the left of the flue exit. It's a 1" port. And here is where my circ is located. Never mind the mess this was during the summer when I was changing things. Any help would be great thank you.