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What should I set my PSI regulator to?

cloudd Member Posts: 48
edited August 2023 in Radiant Heating
For a closed loop radiant floor system using HelioPEX running off of a Combi. 

What should I set the regulators’ PSI to? In other words what should my pressure gauge be reading when the closed loop is charged with water?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,123
    That depends on several factors. I remember that one boiler would not operate unless the pressure in the system was above 18 PSI. But if your boiler does not need a minimum pressure of more than 12 PSI, then you should be good to go at 12 PSI cold fill pressure.

    Another factor is how high the water needs to go above the boiler. Are you sending the water up to the 5th floor when the boiler is in the basement? Then you will need more than 12 PSI. If you are in a building that is 2 stories (plus a basement) then the 12 PSI is all you need.

    Since most auto feed valves for residential heating systems are factory set at 12 PSI and most expansion tanks for residential heating are pre-charged at 12 PSI, then I would just go with 12 PSI. It is a lot easier that way. You want to use good design practices in order to cause air to leave the system via the main air vent near the boiler. that would be pumping away from the expansion tank that is located on the Hot or Supply side of the boiler piping.

    More research is needed by you based on your question.

    I hope this helps.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Mad Dog_2
  • cloudd
    cloudd Member Posts: 48
    The combi is in the basement, supply heated water to the 1 floor  above.  The regulator was set at 25 psi by the plumber. I think it is too high. This is the reason I am asking. The radiant closed loop side of system is not functioning correctly yet. I only have the closed loop working in a primary loop at the moment.

    I have bled the system and currently the system is at 25psi. Seems high from what you are saying…hmmm?
  • GroundUp
    GroundUp Member Posts: 1,926
    In a system like that, 12 psi is standard. The tanks typically come precharged to 12, and the water pressure should match the air pressure. 25 is dangerously close to 30, where the relief is likely to let go, which is a bad idea. Unless the installer changed the relief to 50psi for some reason and charged the tank to 25, this needs to be adjusted. There is no functional reason for the system to be above about 6-7 psi, but since the tanks and fills are typically set to 12, that's standard. Maybe ask the plumber why he did this, and go from there.
  • cloudd
    cloudd Member Posts: 48
    Here are my reading and the and pictures of the regulator and pressure relief valve (max 30 PSI). The system is filled and connected in a closed loop but the manifold is not functioning with thermostats/actuators yet because I have not set that up yet. The plumber has just set the psi on the regulator to 25psi. He does not do radiant floor setups. Usually radiators. That might be why. I was able to lower it to 12 PSI.