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Weil McLain Boiler Sitting at 50 psi?

Rainmaker8 Member Posts: 1
edited November 2023 in Geothermal

I recently had a new boiler installed at the beginning of the year and noticed that my pressure gauge (which is new) stays at 50 psi. My house is approximately 1800 sq. ft., a two-story rambler with three separate zones, and the boiler is located on the bottom level.

In an effort to troubleshoot and see if I could lower the pressure, I manually tripped the pressure relief valve, which released a significant amount of water. After doing so, there was a slow drip for a period of time. The dripping eventually stopped over the summer when the heat was no longer in use.

When I turned on the system this winter, it started dropping again (not always, just intermittently), so I called a plumber who had me drain the expansion tank, which was full of cold, dirty water.

The dripping has since stopped, but the psi remains at 50 psi. The automatic fill valve is always open (is that correct?), and the expansion tank was never replaced (perhaps not needed?). However, from everything I’ve read online, 50 psi seems high (and is also the max MAWP) so I’m wondering what to do about this.



  • WMno57
    WMno57 Member Posts: 1,349
    Hi Rainmaker8, welcome to Heating Help. The white needle shows system pressure, which in your case is 21 PSI. The red needle is a user settable "redline" You can set your redline wherever you like with a screwdriver.
    If you post some pictures of your expansion tank AND THE PIPING BETWEEN THE BOILER AND THE TANK, we can give you some more advice on that.
    I DIY.
  • realliveplumber
    realliveplumber Member Posts: 354
    I see 22 psi, but who's counting lol.
  • ferrociousghandi
    ferrociousghandi Member Posts: 4
    I see 22 PSI also. You might bite the bullet and install a new expansion tank. Yes, they absolutely are necessary. Yes, the valves to the water feeder should be open. If there is a valve going to the expansion tank then that should also be open so that pressure buildup has a place to go. 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,128
    Looking at the boiler rating plate, that boiler is rated for 50PSI max operating pressure. You man need that higher that usual pressure rating if the building is 4 or 5 stories tall. The installer wisely placed the red line at 50 as a "don't want the white needle to go higher that this" mark to remind future service techs that the boiler may require a 50 PSI relief valve if the valve even needs to be replaced. And the cold pressure might be higher than the normal 12 PSI for the standard 2 story home so a new Extrol tank will need to be adjusted to maybe 23 PSI. also the auto feed may need to be adjusted to 23 PSI

    Take a look at these two slides from my Hydronics class

    The cold fill pressure for the taller building must be higher that 12 PSI or you will not get water to the top radiator.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?