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System pressure rising

Jimbo_5
Jimbo_5 Member Posts: 218
Installed a new expansion tank, old one failed, now wondering about system pressure. Set to 12# when cold, rises to 17-1/2 # when hot, 150 degrees. But only goes back to 16# when cool. Last night I drained off 2 quarts of water to get back to 12#. But system was shut down this morning reading 0 psi. I opened the auto feed for a split second and the pressure shot right up to 12#. It has run fine all day, rises up close to 18# but only returns to 16#. Triangle Tube Prestige 110, installed about 12 years ago, 9 cast iron radiators on an old gravity system with 2" pipes circling the basement feeding 1" risers to radiators. Delta T is 30 degrees. System runs for about 45 minutes to satisfy the the T stat. Seems strange to me.

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,935
    edited January 2021
    Your feed piping may be in the wrong place. Is the auto-feed valve on the inlet side of the circulator pump? AND Is the expansion tank on the discharge side of the pump?

    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • Jimbo_5
    Jimbo_5 Member Posts: 218
    There is a spirovent on the return piping attached to the feed water and the expansion tank coming off the bottom. At the time, I believe it followed the piping diagram from Triangle.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,112
    @Jimbo_5

    I think your fine. The pressure in the expansion tank and the bladder position and the water heating and cooling and you may have a little air still trapped in the system from changing the tank.

    The pressures are not always textbook. Just keep your eye on it don't add water or drain let things settle out. Rising from 12-18 from cold to hot is completely normal
  • Jimbo_5
    Jimbo_5 Member Posts: 218
    Thank you, Ed. It may well be air trapped somewhere in the system. I tried to vent all the radiators today, just to be sure, but the darn key broke. Went to Home Depot to pick up a new one but they didn't have any. They didn't really know what the heck I was looking for at first. Right now, the pressure rises up to about 19 psi at fully hot and drops to about 15 when cool.

    The crazy part was this morning when the gauge read 0, yet when I cracked the feed isolation valve (and you know how slow the feed valve is when not forced open) it rose to 12 is a second. So, I think the system was full, just needed a little uumph. But what do I know...
  • Jamie Hall
    Jamie Hall Member Posts: 20,435
    The pressure rise your seeing is not excessive -- but the zero reading is odd. Can you rig up a way to check it with a different gauge?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • neilc
    neilc Member Posts: 2,086
    sound like the gage is sticking?
    try tapping on it next time it's at zero, before bumping the feeder,

    then, why is it getting to 0?
    can you post a picture showing the tank, feed, and circ, all together, boiler too?
    known to beat dead horses
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,112
    @Jimbo_5

    Something seems off. If the pressure ranges wildly from low-high when the water is heated and then goes high-low when it coos that the expansion tank. But I can't see 0. I agree the gauge may be to blame.

    You can get a gauge with a fitting and screw it onto your boiler drain valve to check to see whats going on without draining the boiler
  • Jimbo_5
    Jimbo_5 Member Posts: 218
    Thanks for responding. I will take a picture of the gauge and piping. The small boiler-mounted gauge seems to match the one I mounted at the makeup water and spirovent.
  • Jimbo_5
    Jimbo_5 Member Posts: 218
    Even thought I started out at 12 psi, the system continues to settle on 15 psi after cooling down from heating. I don't get it. I has picked up 3 psi along the way from somewhere. The makeup water was shut off after filling to 12 psi.


  • Jamie Hall
    Jamie Hall Member Posts: 20,435
    The system pressure is going to be a balance between the expansion tank air pressure and air volume and the system water volume. The latter changes with temperature, and so, as the temperature rises the pressure much also rise, as the air gets squeezed in the expansion tank. As the system cools, the water contracts and the pressure drops as the volume of air in the expansion tank increases to compensate.

    Let it sit or a while, and the pressure will stabilize at whatever it will be -- and in this case, it would appear that that pressure is 15 psi. If you want the static pressure to be something else, you are going to have to change the pressure of the air in the expansion tank and, most likely, adjust it once you have (consider: if you set the expansion tank to X psi with the tank empty -- the recommended practice -- and connect it back to the system, if the system water volume then drops further (say the system was warm), the pressure in the tank can't decrease -- it's already expanded as much as it can -- and so the system pressure is going to decrease -- perhaps quite far (it can even go into vacuum, depending on the initial and final temperatures). Therefore, ideally, the expansion tank should be precharged to slightly less than the target system pressure cold -- and the system, as a whole, adjusted to the desired cold static pressure with the tank attached.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England