Boiler getting overpressurized -- reaches 30 PSI and PRV releases water
I just bought a house in August that has a boiler. Iíve never had a boiler before Ė what little I know, Iíve learned from reading the excellent posts on this forum, as well as a few other websites. I have a problem with pressure, and would really appreciate some help.
Hereís the brief description of my problem: My boiler runs at a constant 16 PSI during the day when the heat isnít on. At night, when the heat kicks on, the boiler runs up to 30 PSI and triggers the pressure relief valve, draining water out. It also makes a fair amount of noise Ė some of the pipes are making loud knocking sounds, and thereís a much quieter knocking coming from inside the boiler. Based on what Iíve read, Iím guessing that most or all of the symptoms Iím experiencing are because the system is becoming overpressurized. Iím trying to figure out why.
Other information: Itís a Burnham P209. Itís installed in a closet in our finished basement. A note written on the wall in the closet has the date 9/12/88 and indicates that it should be run at 23-25 PSI. I presume 1988 is when it was installed, although I donít know that for sure. The house was expanded significantly around the same time Ė 7/20/88 is when the building permit for the expansion was granted. It would make sense that a new larger boiler would accompany the expansion. The house is 3600 square feet, three floors, and has a four-zone heating system.
I have an Amtrol Extrol 30 diaphragm expansion tank. From what Iíve read, overpressurization when the water is being heated seems to most often be related to a problem with the expansion tank. I did a simple test on the tank, touching the outside of it while the system was under high pressure. Roughly the top 1/4 of the tank was hot to the touch, and the bottom 3/4 was cool, indicating that the bladder is still holding air. I donít know of any other quick tests I can run on the expansion tank.
Thereís a pressure and thermometer gauge on the outgoing pipe, right after the water comes out of the boiler and just before it goes through the expansion tank. Thereís also a pressure and thermometer gauge on the left side of the casing around the boiler. These two gauges give very different readings Ė the gauge on the pipe reads higher for temperature, and the gauge on the boiler reads higher for pressure.
When the boiler heated up tonight, the gauge on the pipe got up to 31 PSI and 210 degrees. The gauge on the boiler reached 38 PSI and 185 degrees. When the gauge on the pipe hits 30 PSI, water starts getting released by the PRV, which is rated 30 PSI, so that seems to confirm the PSI reading from the pipe gauge. I donít know which temperature reading is correct.
Around 200 degrees on the pipe gauge, the boiler shut off, but the temperature continued rising to 210. After that, it dropped down to about 160, and the boiler went back on, taking the temperature back up to 195 (175 on the other temperature gauge). The pressure again went up to 30 PSI, releasing more water. Itís not a lot of water getting released each time Ė Iíd guess less than a cup.
There are two things I suspect may be going wrong here:
1. Primary issue: The system is getting up to 30 PSI, triggering the PRV. My quick touch test seemed to rule out a complete failure of the expansion tank Ė the tank isnít full of water. What could be causing the pressure to rise so much?
2. Secondary issue: Temperature probably shouldnít be reaching 210, so it seems like thereís a problem there too. Could be that the temperature gauge on the pipe is reading too high, or it could be that I need to lower the high temperature limit on the aquastat. (The aquastat is a Honeywell L8148E.)
Iíd really appreciate any help on what to try next to diagnose and solve this problem! Thanks a lot!!