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.

Pressure drops to zero during cycling

Budd
Budd Member Posts: 11
Hi there. This is my first post. I hope its ok. I've got a 600 sq.ft. garage with in floor heat. All insulated and I have it at 63 degrees. works great I heat it with a 4500 watt water heater. Three 200 ft loops. My pressure goes to zero ( or near zero) when it is in cycling mode. I've tried to pump it up but can only get to 15 psi. It stays there until it cycles. Goes to zero and when it stops it goes back to around 15 psi. Any thoughts? Thanks.
 

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,713
    edited January 2021
    What pump are you using? Is the gauge on the inlet of the pump or the discharge of the pump? Where is the expansion tank in relation to the pump and the heat source?

    A picture or a diagram would help
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Budd
    Budd Member Posts: 11
    Here is a pic of the board. My pump is a submersible. Maybe they don't go past 15 psi??? Thanks for the help Edward.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    edited January 2021
    Sounds like an expansion tank issue. Take another picture from farther back. Is the pressure gauge on the pump suction or discharge?
  • Budd
    Budd Member Posts: 11
    Its on the suction side. I'm trying to pressurize itwith a 1/4 horse utility pump. Is it the correct one to use?  I was thinking about fabricating a small tank that I could fill with fluid and pressurize to  40 psi  and hook it into the system, open the valve and it will pressurize the system a bit. Sounds crazy right?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    We need to see more piping
  • delta T
    delta T Member Posts: 884
    Do the pipes coming out of the bottom of the pump/exp tank assembly go to the manifolds for the in floor tubing?
  • Budd
    Budd Member Posts: 11
    Ok, more cowbell haha. This is the hot water tank also.
  • hot_rod
    hot_rod Member Posts: 22,018
    If the pump is flowing down, look for an arrow on the body, then the expansion tank should connect to the red handle valve near the pump. In my mind. 
    The exp tank precharge pressure could be set at 12 psi, then fill the system to 12 psi
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    delta T
  • Budd
    Budd Member Posts: 11
    They go to the manifolds.
  • Budd
    Budd Member Posts: 11
    You can see that I have 16 psi right now.
  • Budd
    Budd Member Posts: 11
    Thanks Bob, the tank says its pre charged to 12 psi. It also says working.pressure 75 psi. And I have 14 psi but the gauge could be out.
  • Budd
    Budd Member Posts: 11
    Also, the expansion tank is the last thing before the fluid goes into the hot water tank.
  • hot_rod
    hot_rod Member Posts: 22,018
    16 psi static, drops to0 when the pump runs?
    Which pump setting are you on? Try speed 1 see how it changes pressure. As I see it you are pumping at the expansion tank, should be pumping away,
    Was the panel built that way?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Budd
    Budd Member Posts: 11
    Yes it was. Came from the company that way. I'm on an auto setting. I can try the number 1 setting and see what that does.
    Thanks again.
  • Budd
    Budd Member Posts: 11
    Yes, I see your point and never thought of that. I may rig up a pressure gauge and put it in different places in the system to see the change when its active versus static. it'll be a good learning experience. It doesnt appear to be hurting anything. Thanks, great forum
  • hot_rod
    hot_rod Member Posts: 22,018
    yeah, you really do not want the pressure at the pump inlet to drop to 0 psi. All pumps, even small residential have a NPSHr, minimum psi requirement at the inlet. I think something like 1.5 psi at 140F for that pump, no harm in seeing more pressure. Pulling to 0 or below invites cavitation, not a good condition.
    Personally I would move the expansion tank, pressures will be better and air removal improved.

    Or you could remove the tank, pump it to 20 psi, reinstall and pressurize the system to 20 psi, then you may see 5 psi or more at the gauge when it is running.

    Not sure if you are looking for a work around, or the best solution?

    Static pressure is the pressure you fill to and observe when the pump is off. Dynamic is the pressures you see when the circulator is running. You'd like to see positive pressure in all parts of the system when it is running. The pump head added should show up in the gauges.

    Here is a graphic showing how the expansion tank connection affects the pressure in the system.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Youngplumber
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    You need to repipe the expansion tank to where the ball valve is on the pump suction.

    A system with the restriction you have has to pump away from the expansion tank. You do not have that now.

    You want the system restriction to be on the discharge side of the pump not the suction side
    Youngplumber
  • Budd
    Budd Member Posts: 11
    Thanks a lot for the posts. Very educational. I will try that setup.