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Posted by Harold hydronicnetwork.net on February 04, 2004 at 08:21:42:
In Reply to: Percolating boiler, can't seem to bleed air out. posted by Matt on February 04, 2004 at 07:34:24:
Percolating is not an air problem in a filled system. When water flow is too low, the water boils within the boiler and the steam bubbles collapse making the pinging and sizzling as during cavitation on a circulator. It could be dirt or casting pockets, but most of the time it is due to low water flow with multizone systems shutting off much of the radiation, so less water than is needed to cool the boiler is available. Sometimes, a bypass must be installed on the boiler to increase flow. Sometimes, just permanently raising the pressure in the boiler will stop percolation.