my hw furnace pressure goes to 30psi despite having a15 psi expansion tank and 15psi regulator?

Answer 1

Is it a new boiler.??? If it is old the expansion tank may be waterlogged. The bladder croaked. If you bleed a little(very little) air out through the valve at the bottom, and you get ANY water, replace the tank..If that is not the case then you have a bad boiler feed( regulator) Replace the regulator(boiler feed).

Answer 2

Well, either the pressure gage is wrong or the pressure safety valve should be squirting water if the regulator was not limiting the pressure to 15. (The regulator is on the fresh water inlet from the city or your pump if you have a well.)

Not sure how the expansion tank relates to 15 PSI? Most don't have an air balanced bladder, like a well pump setup would have in its expansion/pressure tank.

Answer 3

is your expansion tank one of the big old ones that is mounted up in the ceiling? if it is, it sounds like it is full and needs to be drained. i have the old cast iron type radiators and a huge tank strapped up on the ceiling. i had to drain it this year, i have to do it every few years. if you have one of the little gas grille sized tanks, it could be that the bladder has gone bad or you don't have any air on the other side of it. not sure how you fix that, but your furnace service tech should be able to tell you how. good luck, hope it's a simple fix for you.