I wasn’t sure what title to give this but hopefully the right people will see it and help. I have a Tarm Excel 2000 with Tarm’s standard plumbing setup Figure “E”. http://www.woodboilers.com/userfiles/file/Excel Plumbing(1).pdf C-1 and C-3 are both 3 speed grundflo pumps the rest are Taco 007’s. Now that I have my handy dandy IR laser guided digital thermometer I’ve been checking the temp of everything, inlet water, storage tank, outlet water, the cat etc. What I’ve found is that when the boiler is running and supplying hot water to the house I’m also getting some water out of the storage tank bleeding in. It goes like this: water coming out of the boiler is 170, water at the top of the tank is 160, the water that is actually going to the house is (measured after the “T” that ties in the loop from the storage tank) is 166. I’ve verified this by shutting off the storage loop and watching the temp climb back up to 170. Now this isn’t a big drop but what’s also happening is that the return from the house which is 145 is entering the storage tank from the bottom heating up to 165 and back to the house which I didn’t need in the first place. I don’t see how any of this is good, the water to the house is cooler which means it takes longer to warm the house, my storage tank is dropping which means I’ll have to burn more wood to heat is up again. Am I missing something? I have the 2 back flow preventers (see diagram) which are supposed to prevent siphoning but the pump seem to be overcoming them. It seems what I need is a normally open valve in the storage tank line, which is only closed when both the boiler circ pump (C-3) and house circ (C-1) pump are both on. I think I could do this with two relays in series. Anyone else have this issue?