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Posted by Charlie on February 13, 2005 at 08:15:57:
In Reply to: Re: Help posted by HeatPro on February 11, 2005 at 19:26:21:
Will try raising pressure to 18. What is meant by installing a bypass at boiler? And yes i have 7 zones with one being indirect hot water. The one zone than goes on over night mostly is the master bedroom where i have it come on and raise temp for wakening up.Seems as if I may be keeping other zones too low so not much flow. Thanks for your assistance as always.. : 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.
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