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Old 10-10-12, 01:40 AM   #8
Lurking Renovator
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this is the same system as ice rinks. there is usually a shut-off valve at each return location, usually every year or so at start-up most returns are shut off to keep all pipes pressurized and a main header drain is opened or the air eliminator in the system will remove air which becomes lodged in one of the pipes. Usually most hydronic system will have some air migrate into the pipes through the non-heating season. At the initial start-up the (sounds like a river in my pipes) air will be pushed into the expansion tank. The more parallel runs, the more chance of cold spots.
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