Yes, I meant soldering a copper fitting after it was made up to a threaded fitting. I figured you didn't do that but I had to ask. My apologies
If I had to guess id also say the seals at the circulator could be were some slight amount of air is leaking
I have radiant heat in my kitchen, a small section were the sink and cabinets of my kitchen is over a crawl space and it was always cold there, we ran some of the tubing actually under the floor there now its warm and comfortable on even the coldest days
