(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 6 of 6

Thread: pressure relief valve blows off at 20lbs

  1. #1
    DIY Junior Member jpaul's Avatar
    Join Date
    Apr 2009
    Location
    Connecticut
    Posts
    15

    Default pressure relief valve blows off at 20lbs

    Heat running, pressure builds to 20lbs, blows off some water until it builds back up to 20lbs and blows off some water again. Bell & Gosset expansion tank (2 years old), 11-12 year old boiler w/coil. Boiler temp was increasing from 175, 180, 185, 190, 195. Pressure never went beyond 20lbs and blew off some water every time once it hit 20lbs. I checked 15 minutes after I turned heat off and boiler not running. Boiler temp 205, 12lbs pressure. Settings at 140 & 180 degrees. Thanks for looking...Suggestions?

  2. #2
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
    Join Date
    Mar 2011
    Location
    Minneapolis
    Posts
    285

    Default

    Had the boiler serviced by a professional lately?

    Fill valve on?

    Pressure relief valve tested or replaced in the last 5 years?

    Expansion tank full?

  3. #3
    DIY Junior Member jpaul's Avatar
    Join Date
    Apr 2009
    Location
    Connecticut
    Posts
    15

    Default

    Quote Originally Posted by BadgerBoilerMN View Post
    Had the boiler serviced by a professional lately?

    Fill valve on?

    Pressure relief valve tested or replaced in the last 5 years?

    Expansion tank full?
    Thank you for your reply. I have a cleaning annually. I believe the fill is an auto fill. When I tap the expansion tank top and bottom with a wrench sounds about the same. The top of the tank feels warm and the bottom feels cool.

    I just changed the relief valve and the boiler pressure goes up to 25 lbs and does not blow now, however I don't know if the boiler is operating properly.

    With two zones calling for heat the boiler temp was 170. I turned one zone off and the temp started rising. The temp went to 200 degrees and the burner turned off but the thermostat was set for 76 and was reading on 70 when it turned off.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,382

    Default

    Depending on how the boiler is set up, the thermostat may control the circulator, not the boiler. The boiler may be turned on by an end switch on the circulator or zone valve, but it may cycle up and down between the min/max aquastat settings on the boiler. IOW, it may be normal for your boiler to shut down while there is still a call for heat if it bounces off the max temp. If the pressure varies a lot between cool and hot, the expansion tank is suspect. the whole idea of the expansion tank is to moderate any changes. 25# is a little high for most systems, but could be okay for yours. More typical is in the 12-15# range. If the expansion tank rings when you hit it, the bladder is not likely shot, but the static pressure may not be set properly. To set the static pressure on an expansion tank, you have to depressurize the boiler otherwise, reading the pressure on the expansion tank will be exactly the same as the boiler pressure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Junior Member jpaul's Avatar
    Join Date
    Apr 2009
    Location
    Connecticut
    Posts
    15

    Default

    Seem to be ok since I replaced the relief valve. Thanks for the help.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,382

    Default

    Many residential systems use a 30# relief valve in their boilers. While there may be lower ones and there are higher ones, if it's opening at 20#, it is, as you found, the most likely suspect. But, with a properly sized expansion tank, precharged properly for your system, the pressure should not vary much during operation. Your expansion tank may be too small, or it may not have the proper pre-charge.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

Similar Threads

  1. Necessity of Vacuum Relief Valve - Not Pressure Relief Valve
    By WillieK in forum Water Heater Forum, Tanks
    Replies: 67
    Last Post: 11-17-2013, 09:58 AM
  2. cut-in/cut-off pressure 20lbs differnece
    By ugabulldog in forum Pumps and Tanks Well Forum & Blog
    Replies: 10
    Last Post: 03-06-2011, 07:55 AM
  3. pressure relief valve
    By rbig in forum Irrigation / Sprinkler Forum
    Replies: 2
    Last Post: 05-24-2010, 11:12 AM
  4. pressure running at 20lbs
    By horseshoer in forum Pumps and Tanks Well Forum & Blog
    Replies: 9
    Last Post: 11-14-2006, 06:13 AM
  5. Pressure Relief Valve
    By terrell44 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 2
    Last Post: 04-14-2005, 11:25 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •