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Posted by HeatPro on October 28, 2004 at 10:30:16:
In Reply to: circulator pump for add on infloor heat posted by jtwieck on October 27, 2004 at 18:33:42:
The most likely cause is a lack of a flow control (weighted check valve0 on the line from the radiant loop circulator. The other pumps force water backwards against the pump without a check valve.
http://64.226.150.132/hydronic/multcirc/multcirc.htm
Another cause would be using a high-head pump (over 11 feet head), which is unnecessary.