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The main vents squirt water

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Published
July 10, 2009 Subscribe to RSS feed

They're either in the wrong place, or they're dirty.
You'll find end-of-main vents near the ends of the mains on gravity-return, two-pipe systems. You'll also find them near the bottoms of the return risers. Make sure the vents aren't in a place where water hammer can reach them. Ideally, they should be at least 15 inches back from the end of the main, and at least six inches up on a nipple.
Since gravity-return systems have no vented condensate- or boiler-feed pumps, the only way for air to escape is through the main vents. If the boiler pressure is too high, water will back into the vents and make them squirt. Crank the pressure down, and you should see a difference immediately.
Also, since the water leaves sediment in the main vents, you may have to boil the vents in vinegar for an hour to clean them out. If that doesn't work, the vents may have been damaged by water hammer. Replace them.