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Posted by HeatPro on January 27, 2007 at 13:35:18:
In Reply to: Percolating in Boiler posted by Chris on January 27, 2007 at 12:04:24:
Percolation happens when the water through the boiler is insufficient to take the heat away from the boiler, so the water overheats to steam bubbles.
That is a result of zoning with zone valves. When you close off some of the passages that water is to flow through by having zones closed, insufficient water passes through the boiler.
This can be solved in a few ways:
A HeatManager control can be installed to keep the water just hot enough for the weather.
http://www.becketthm.com/
An outdoor reset control can be used to keep the water temperature to just enough for the weather.
Water flow can be increased and held to a minimum through careful installation of a bypass pipe around the boiler (usually a half-inch line with throttling control valve is sufficient for residential systems.)
One zone can be held open all the time with no boiler firing thermostat, like a bathroom zone, which will function like a boiler bypass to allow a minimum water flow.