carlherrnstein wrote:I would imagine that its normal for the pressure to drop when the circulator pumps come on because liquid water expands when heated and contracts when cooled. The water in the boiler is hot and expanded(higher pressure) then the pumps come on and the boiler water starts to cool off and contract(lower pressure)
However I'm not a hydronic guy an this is only a hypothesis.
Sting wrote:long read - but this question will need it...
http://www.heatinghelp.com/article/343/ ... ure-Change