frank1492 wrote in
:

I have a closed hydronic loop with no obvious leaks in a boiler
heating system. The expansion tank is quite old. Lately I noticed the
pressure dropping even when the circulator is not circulating. What
starts out at 15 psi will be down to 7 by the end of the day. There
are no known leaks anywhere in the piping.
While the expansion tank seems to be the culprit by a process of
elimination, some signs point otherwise. For example, when I let water
into the system the gauge rises slowly as if the bladder is expanding.
Also the top of the tank is warm (when the therm calls for heat) and
the bottom seems cold which suggests the bladder isn't leaking..
Before I replace the tank, could someone give me their thoughts
on this? I sincerely appreciate your help.
Thanks.
Frank


We searced for such a leak for 2-3 weeks.
Turned out to be inside the unit, leaking into
the condensate dump pipe.