I have a gas fired, baseboard hot water system in my house, that I installed myself, 25 years ago. Other than a couple of zone valve problems, it's been trouble free. It still works fine, except it started dumping/dripping water out of the pressure relief valve. Not a big deal I guess. Just make a mess on the floor. Had to stick a bucket under it. Any ideas? Too much incoming pres, expansion tank??

Sounds like the expansion tank. Is it a bladder type with a schrader valve at one end? If it's not a bladder type it will need to be drained. Shut the valve to the expansion tank and drain it, it may take serveral times to drain it.

Boiler pressure should be 12 when cold and no more then 20 psi when up to temp

Bill... Here's a shot of the expansion tank. It is the type with a bladder. I assume now, that the bladder has leaked, and the tank is now full of water? ...So it's dumping the excess out of the pres relief? Can I just unscrew the tank, and screw the new one on, or do I have to turn everything off, and drain the system?

http://i533.photobucket.com/albums/ee335/wrrose/100_2228.jpg

Bill:
My hot water tank had a HISSY-FIT (pressure pop off) a few weeks ago, After screwing around, My incomming water press. Should have been 55 PSI --it was 105 PSI. My press. Regulator on the main line from the street went south. I bought a gauge $7.00 screwed it on to laundry tubs for at LEAST --20 min. Press went up, I went to home depot! That was my fix..........
Bob

Bill,

Yes, that is a bladder type. If it full of water it will need to be replaced. If the water is hot you can just feel the tank it should be hot about 1/2 to 3/4 and cooler towards the bottom.

If you give the valve a quick purge and water comes out it is bad.

Since there is not a shut off valve before the tank I would shut the boiler off and get it cool. Shut the supply water off to the boiler and just bleed the pressure off.

Then change it on the fly. You may get a little wet, or you can drain it down if you feel more comfortable. Be sure the water is cool if you do it on the fly.

As the rest have said expansion tank is water logged.

Funny thing we just rebuilt the hot water heating system at work. 18 of 24 heating elements out. Unit is 390 kw at 480 v 3 phase.
When putting system back on line the expansion tank also filled up. As the tank came up to temperature, the pressure climbed to high, causing the pop off to release the pressure. Our pop off is set at 50 psi, system normal is set for 25 psi max. Drained system twice before things settled down. Commercial systems are a little different but same principal.
This week we are cutting the pipe work (no unions/ adding them) for a stream humidifier. The auto drain appears to be plugged with scale. Another important thing about boilers!

You might be able to correct the problem by re-pressurizing the tank with air or nitrogen. There should be information on tank as to what psi. Good luck