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Posted by HeatPro on February 11, 2005 at 19:26:21:
In Reply to: Help posted by Charlie on February 04, 2005 at 11:06:42:
Seems you corrected the air problem, but had a new one as you lost the cushioning ability of the air in the loops. The statement that you have several thermostats means that you have several zones. When most of the zones are closed, the flow through the boiler is low as only one zone is open, so the boiler water can get very hot and boil water locally to collapse and make a knock as the water slowly is replaced with cooler. Try raising the pressure to 18 psig and listen if the knowk goes away at night. If that doesn't do it, you might have to put a bypass at the boiler or leave one zone valve open to act as a minimum water flow bypass through the boiler to keep water flow through the boiler up.