Speedy Jim wrote:

Silo wrote:

Hello Can someone help me with a gas fired boiler. I have an old American
Standard boiler that has developed a problem with tank pessure
exceeding 30 psi. which blows the 25 psi pop off valve. And then
returns to 10 - 15 psi for hours at a time and then out of the blue it
builds to much preesure and the safety valve goes off? Coincidence or
not this problem started immediately after a "free" inspection? I have
so far replaced the pop off valve and the water pressure reducing fill
valve. I also notice my Aquastat was set to maximum temp of 200
degrees. Other than the pressure the boiler is working fine. Does
anybody have any ideas?




Be 100% certain that *no* water is being fed to
the boiler, even via a bypass/manual fill valve.
One good tipoff is if the feed pipe feels cool.

If no water is being fed, the pressure should not go up
dramatically, UNLESS the expansion tank is waterlogged.
If it's a diaphragm tank, it may have failed internally.

Jim

I should have added that control failures might cause
high pressure. For example, if the circ pump(s) quit
running and/or the aquastat stuck closed, the boiler
could fire continuously and it would wind up steaming
till the relief went.

Jim