I had a burnham boiler installed a little over 1 yr ago. The service techs have been back a few times to tweak the system. The last time I called them out was because the second floor radiators didn't seem to be getting hot enough. When the tech came out, he determined that the pressure had not been set right during the install. He adjusted the auto fill valve from 12 psi to 19 or 20 psi, saying that 12 psi was not enough to push to the second floor. Every radiator has been getting hot since then. A little while later, I noticed water dripping from the prv. I isolated the auto fill valve to see if maybe that was bad, but the pressure still climbed to 30 psi at which time the prv leaked. I am pretty sure that the expansion tank is the culprit. My question is: the expansion tank is precharged at 12 psi. When the tech upped the pressure on the system from 12 to 20 psi, is that size expansion tank right? I would think it should be at least 20 psi? If a 12 psi tank is acceptable, does it sound like the expansion tank is bad, or could there be another problem? Thanks

Your tank pre-charge should be the same as the setting of the pressure reducing valve. Increasing the pressure on the system decreases the amount of expansion capacity of the tank. Add radiators with their large water capacity & I would suggest at least a #60 expansion tank. Far and away the most common size is a #30. Here's a link to Amtrol's site: Amtrol- Extrol Expansion Tanks

Did he increase the precharge on the expansion tank to match the new system pressure? If he didn't he was setting you up for an expansion tank failure. Also 19 or 20 psi seems excessive for a 2 story house, I assume that the furnace is in a basement. Subtracting 3 psi for pressure margin, I still am coming up with about 38 feet of head. Way beyond necessary. Sounds like your PRV backcheck valve thinks so too. Now at the original pressure of 12 psi - 3psi =9psi= 20 feet of water and unless you have 10 foot ceilings you were OK originally. It sounds to me more like you had air in the system.

To get the correct pressure setting for a hot water heating system you measure the vertical distance between the furnace -where the gauge is- to the top of the highest radiator/heat exchanger, convert that number which is feet of water to psi. 1 psig = 2.3 feet of water. Add 3psi for safety and set your PRV to that number (or factory preset 12, whichever is higher). This is a very basic explanation of setting system pressure. There is a lot more that goes into it depending on the system, but this works for 95% of residential systems.

If the 19-20# is cold fill pressure, I agree, it does sound excessive. Given the mention of radiators (extra height, probably old house [high ceilings], I was thinking of a cold fill pressure of around 15# which when heated could go to 19-20#.

EPMiller: I like your signature line. How true it is.

The boiler is in the basement which is also heated. The house is an older one, around 1935, with 10' ceilings. Made sure to bleed the rads pretty consistently after the install and thereafter. In all there are 11 cast iron radiators in the house. To my knowledge the tech did not increase the pressure of the expansion tank. I checked the pressure again, and it is set at 19 psi when the boiler is not running, but climbs to 30 while running, at which time the prv opens.

Where did my post go?? I have wasted my time several times now when the reply box just loses it. I had a long explanation of what I think is going on for the OP and the reply box just lost it when I was editing. I just don't have time for this. Sorry Matt, but I have other work to do and my wife is starting to ask when I'm getting at it. :-)) Maybe another day.