Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

First pressurization of a new

edited September 2019 in THE MAIN WALL
.........or previously drained system. The x-tank has been charged to 15psi and you open the bypass valve to fill it quickly. You know there's a lot of air in the system, so you want to overfill it to help vent the air. The pressure climbs to 15psi and steadily increases to 25psi.

My questions is: Why doesn't the gauge pause at 15psi as the expansion tank absorbs the increase in pressure above 15psi? Or maybe it does and I'm not noticing.
Often wrong, never in doubt.

Click here to learn more about this contractor.


  • Jamie HallJamie Hall Posts: 12,120Member
    In order to accept the additional water, water has to go into the expansion tank. Which raises the pressure in the tank. No pause -- it will be smooth.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • TomSTomS Posts: 50Member
    I think it does because you are filling at a rapid rate and you don't notice. One trick I used to determine the pressure of high pressure accumulator tanks was to slowly pump up the system and notice the rapid increase of pressure. When the rapid increase slowed down or stopped that was the accumulator tank pressure. Further pumping would then start to increase the system pressure again. This all had to done slowly.
  • nibsnibs Posts: 392Member
    @Alan (California Radiant) Forbes Brought my fill line vertical for about 3 ft, had a spare new air bleeder valve, courtesy Habitat re-store, and put it on a T instead of a 90, where it turns horizontal for the boiler fill I use two ball valves (the one at the x can has the handle removed to try to make it idiot proof, when I open the first ball valve most of the air bleeds off before it goes into the boiler. Also took the handle off the DHW dump valve to cut scalding risks for the Gkids if they get a little inquisitive.
    PS I fill mine slowly right at the x can and it does seem to hesitate as the can takes up the slack.
    Regards to Penelope and Otis.
  • rick in Alaskarick in Alaska Posts: 980Member
    You might also find the bladder in the expansion tank is stuck to the tank. I have had a few do that, which makes it a non expansion tank. I have had to add more pressure to the tank in order to get it to break loose. One way to prove it is stuck is if you have it set up with an isolation valve with bleed port is to put your water pressure in and then shut off the isolation valve. Then open the drain valve on the tank and see if you get your full capacity of water come out, say four gallons or so. If you only get a bit, then it did not accept any water, and is stuck.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!