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What do all three of these gauges measurements mean?

bender1227 Member Posts: 35
edited October 2016 in Gas Heating
I am just trying to understand what all three of these gauges mean and stand for with my boiler system?

It looks like we have a tempature of the water in the system which is the bottom part of the gauge.

On the top I'm assuming PSI is the pressure in the lines but what is Feet H20?



  • Jamie Hall
    Jamie Hall Member Posts: 18,924
    The bottom scale is temperature; the red hand relates to that scale (not the top one) and is resettable by hand; it indicates the maximum temperature reached since it was reset -- although it looks as though someone fiddled it. The top scale is psi (pounds per square inch) on the inside, and the corresponding feet of water on the outside -- the feet simply being how high above the gauge that much pressure could push water.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I have a similar gauge on my W-M boiler. On mine, the white one measures pressure only and the red one does not indicate the maximum pressure at all. I can set it anywhere I want. What I do is set it when it is running normally, but not firing and no circulators are running. Its sensor is in the wrong place, so if the circulator to the indirect water heater is running, the pressure drops, though there are no leaks. It measures the pressure where the sensor is. (Just as a thermostat acts to keep itself comfortable.) I just set it to the pressure the white one shows.

    Now, if the white one drops, I know there is a leak, to the outside (possibly due to a pressure relief valve relieving itself). If it goes up (it never has), I know that either the make-up valve leaks, or the indirect is leaking street pressure into the boiler system.

  • hot_rod
    hot_rod Member Posts: 16,287
    I think the red pointer is just an indicator that you can manually set. Usually just below where the relief valve setting is, ex 30 psi relief valve on the boiler, indicator set to 28 psi.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bob_46
    bob_46 Member Posts: 813
    It's called a theraltimeter or tridicator they still make them. The red hand is adjusted to the distance in feet between the gage and the level of water required in the open "expansion" tank in the attic. You fill the system until the upper white hand lines up with the red one. If you don't have an open system with an expansion tank the red hand is redundant . If you don't have an open system you have a "compression" tank and probably an automatic fill. The bottom white hand indicates boiler temperature.