There is a Weil Mclain boiler (installed in 95) in the house I recently purchased. It's a closed loop system with three zones.
The system has a smaller pipe (3/4 or an inch) that goes between the main incoming and outgoing water lines. The smaller pipe that connects the mains has a lever valve on it (I'm assuming this is the bypass valve). A heating contractor told me the lever should be just partially open to allow some of the water on the hot side to warm up the cooler water of return side before it enters the boiler. The problem is the system is very loud when valve is anything but completely closed or open (causes all sorts of strange surging and clunking noises in the pipes). I had someone else look at the system and he said the valve is usually just partially opened, but since mine was making so much noise it might not hurt to completely open the valve. He didn't seem real sure of himself and now I'm completely confused. Should this connection be completely open or not? If it is left open, doesn't that just bypass the rest of the heating system or, at best, create a lot of inefficeincies? Any help would be greatly appreciated.
My second question is how detrimental it is to run glycol-based antifreeze in a closed-loop system like mine? I'd like to leave the basement zone off, or set very low, but some sections of line at the exterior wall will freeze if I do that (already happened once).
Thanks again for any help. Boiler systems are new to me, and I sure am learning a lot.