I started renovating a room in my house with fin tube radiation. I also have an indirect hot water tank so my boiler heats both my perimeter radiation and domestic water in my storage tank. I have 2 flow control valves on my boiler, one for my perimeter heat and one for my domestic hot water. I tried to shut the valve feeding the perimeter heat but the small handle on top just kept turning and wouldn't stop, so obviously this wasn't going to work. I shut the supply water going into my boiler. I cut out the fin tubing in the room I am renovating. All was good, so I thought. I noticed the circulator pump for the hot water storage tank was constantly running and was VERY hot! It also sounded like it was air bound at times and I lost my hot water. I opened the boiler drain on the return line into my boiler to bleed the air but nothing came out, in fact it was pulling a vacuum. The boiler wasn't firing off either. I finally capped the feed into the room and turned the boiler water feed back on. Everything works fine now. I'm confused as to why I needed the feed water into the boiler on for the hot water tank loop to work properly. Maybe by cutting out the perimeter radiation the system got air bound?