I have a system where the hot water tank is just a storage advice, meaning it's not wired for electric or plumbed for gas, the boiler does the heating. I have in line for the water (potable) a circulator pump that keeps water flowing through the system for quicker hot water at the taps. Now, is this thing SUPPOSED to run all the time? It has a merc switch thermostat right next to it, and it appears to be set to about 150-175 degrees, but it's ALWAYS on. It's one of those things that just get me wondering sometimes. Incedentally, I had some work done about 2 years ago, and that plumber reset the thermostat on it's side, for door clearance, and it never came on. That's when I found out about the merc switch, and after righting it again, it started circulating. Anyhow, what can you folks tell me about that?