I believe you mentioned in your other thread that the replaced the expansion tank. An Issue I had in the past when the diaphram inside the expansion tank came apart, the rubber pieces from the inside of the expansion tank kept getting stuck in the check valves causing them to stick open. The water would keep circulating even though the circulator pump wasn't on. I use to have to take the top of the check valve off and pull out the piece of rubber from the expansion tank. I had to do that multiple times until I got all the pieces out. Either that or you have to have the system flushed.
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