Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Happened more than once.

Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 4,243
in THE MAIN WALL
Replaced an expansion tank and the pressure goes up on a call for heat. It's as though the system doesn't see the new expansion tank.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab

Comments

  • delta T
    delta T Member Posts: 884
    Is the tank sized correctly? Never assume that what was there was correct. Also I have seen feeders go bad when the water is turned off and then back on and slowly creep increasing the pressure slowly.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,243
    I replaced it with the same size x-tank because it was large enough.
    The pressure only goes up when its heating which should rule out a problem with the fill valve, no? This did come to mind, though and I was going to turn off the city water as a test.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • ChrisJ
    ChrisJ Member Posts: 16,360
    This may be a stupid question but, how can the pressure go up if the tank is working correctly? It's impossible, no?

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    Get a dead tank out of the box? I've had it happen. ..
  • delta T
    delta T Member Posts: 884
    I agree. The possibilities are as follows: the connection from the tank to the system is blocked, the tank is under sized, the tank is not properly set to system pressure prior to installation, or the tank is defective. If none of the above are true then the pressure will not go up.
  • JUGHNE
    JUGHNE Member Posts: 11,309
    Is this CI radiation?
  • kcopp
    kcopp Member Posts: 4,486
    does it go into a Spirovent? I have had that happen where it blocks off the top of the tank.
    Bob Bona_4
  • Paul48
    Paul48 Member Posts: 4,469
    I was going to ask where I could get one of those tanks. :smile:
    From my experiences.....the pressure will always slowly build, and stop below the point at which the PRV discharges, as long as the tank is sized correctly and everything is working correctly.
  • ChrisJ
    ChrisJ Member Posts: 16,360
    Steam is so much easier when you know how to use it.
    No bladder tanks, no pumps, no bleeding, no problems!

    Sorry.

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

    Bob Bona_4
  • delta T
    delta T Member Posts: 884
    Well okay, I didn't mean that it would not go up at all, It will always go up, just within the bounds of normal parameters. I typicallay do not see an increase of more than 5 psi from cold start to operating temperature if everything is sized correctly. Occasionally more, but if you set your static fill pressure to 12-15 psi for the average residential system, I would not expect the pressure to go up to more than 20 psi. I should have been more clear, my apologies.

    @Paul: they are magical tanks, you have to pay extra for the little gnome to carry the small buckets of water to the nether dimensions and back as the water expands and contracts! They are made by the same people that make the magic smoke that electrical motors and transformers run on. Contrarty to popular belief the electricity is what keeps the smoke in. :)

    JUGHNE may be on to something, I have seen high mass systems like CI radiators or large thick radiant slabs have higher expansion tank requirements than I anticipated, due to the large thermal mass of the system. Although if someone would like to elaborate on the physics of that phenomoenon I would be interested.

    I feel like it is because the extra thermal mass acts as if it were another heat source and there are times when the mass is up to temperature and is dumping heat into the system water, at the same time as the boiler, thus making the water see more of a heat source than just the boiler, necessitating a larger expansion tank. I have never actually looked this up however and I would love to get a definitive answer!


  • Paul48
    Paul48 Member Posts: 4,469
    No......when you've had a problem, you haven't figured the volume of water correctly. It's not possible for the mass to heat the water to a higher temperature than the boiler. I think the gnomes may have been smokin' somethin'.
    Rich_49
  • delta T
    delta T Member Posts: 884
    just curious. I have had a couple of old system retrofits with CI rads and one radiant floor that was steel pipe in the concrete. I must have mis calculated the volume. I know the system cant heat over the boiler, just thought maybe there was a total excess of heat at some point, but then again, all the btus ultimately came from the boiler to begin with...hence the question. It is pretty rare that I run into that problem and increasing the size of the tank always solves the problem. Thanks for the clarification!

    I am in Colorado, so our smoke is pretty magical :)
    vaporvac
  • delta T
    delta T Member Posts: 884
    Thanks!
  • hot_rod
    hot_rod Member Posts: 23,785
    Occasionally the bladders stick inside the tanks, maybe increase the pressure for a minute and see if you hear a pop
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    RobGrick in AlaskaCharlie from wmass
  • JUGHNE
    JUGHNE Member Posts: 11,309
    The CI rads inquiry was because some 2nd floor rads not completely bled of air can constitute additional air cushion.

    In one case it was the only air cushion and when the air was bled later in the season the PRV would open.

    I'm caretaker of boiler systems for a church, the Rectory house is not lived in. Only used as day time office. The second floor rads are not bled completely for the reason of not heating that floor. Just maintain water movement along the lower sections.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,243
    Thanks, guys. I like Hot Rod's suggestion that the bladder might be stuck. I remember when the system was fully pressurized and I opened the ball valve at the expansion tank, there was no sound. I'm going back on Tuesday and will fiddle with the pressure.

    xxoo

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    Charlie from wmass
  • RobG
    RobG Member Posts: 1,850
    Alan (California Radiant) Forbes said:

    Thanks, guys. I like Hot Rod's suggestion that the bladder might be stuck. I remember when the system was fully pressurized and I opened the ball valve at the expansion tank, there was no sound. I'm going back on Tuesday and will fiddle with the pressure.

    xxoo

    Several years ago ME broached the subject as he has had it happen more than once. I believe what he stated doing was adapting a Schrader valve to the tank inlet and putting air pressure into the water chamber until it broke free. You might want to PM him.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    The butyl have a wrinkle and got stuck?

Categories