Originally Posted by beenthere
Most likely an inaccurate pressure gauge. What kind of expansion tank do you have. is it a bladder tank, or a big steel tank.
It's a modern steel bladder tank (Watts). The top of the tank doesn't seem to get warm (or any part of it) even after the boiler has been operating for some time and it sounds empty though I'm not experienced in what it SHOULD sound like when tapped at the bottom.
I don't have a bicycle pump (really thinking about braving the rain out there and getting one because this is bothering the snot out of me) and I don't want to use my car tire gauge because it tends to suck and let a lot of air out before I can get a seal on it without having anything to fill it back up again so I haven't done any kind of pressure test on the tank.
There is no valve in line with the inlet to the tank, the only valve is upstream of it past the reducing valve and backflow valves. All I know is that when the boiler temperature is reading below 100F and I trip the relief valve water refills the system and eventually it stops out at reading approx. 25 psi which seems insane. I have released the pressure a number of times between heating cycles and it always goes back. Other than the gauge giving me the creeps the heating system seems to be working normally with no abnormal pipe noises or leaks at any of the rads (which are all less than 8 years old, same goes for the boiler itself). The actual pressure reducing valve's top nut isn't loose or anything so I don't see how it could have gone out of adjustment by itself.
I'm feeling it's probably not safe for me to fiddle with this much more, though the tinkerer in me really wants to force open the reducing valve to see when exactly will the relief valve automatically purge.