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Rinnai i120sn expansion tank pressure

dough041 Member Posts: 28
Just on the home stretch on my install of a Rinnai i120sn heat only boiler. The question I have is the manual indicates the usual operating pressure for this unit is 14-17 lbs of pressure. The extrol expansion tank I plan on iinstalling is prescharged at 12 lbs. Should I up the charge on the tank a couple lbs to match it or am I wrong? Any help is appreciated…


  • Jamie Hall
    Jamie Hall Member Posts: 22,897
    That depends on how high your highest radiator is. 12 pounds is generally good for 15 feet above the boiler. Set the pressure reducing valve to the same pressure.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • dough041
    dough041 Member Posts: 28
    I run hot water baseboard…so I should adjust the PRV to the same pressure?
  • hot_rod
    hot_rod Member Posts: 21,835
    They need to match. So raise the tank or lower the fill pressure 

    Good idea to check the tank. They are not always what the label states
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,525
    edited August 2023
    Does the boiler have a minimum recommended operating pressure? I remember when I installed my first Buderus ModCon many years ago, there was an error message on start up. "pressure too low". (of course I checked the Gas pressure and it was fine) I then went to the I/O manual and found that the boiler required a 17 PSI minimum water pressure to operate. This was for space heating only. If the water pressure sensor was lower than 16.5 PSI the burners would shut down and the error message would display.

    You only need to experience that once. I liked the boiler, so on each boiler I installed after that, I added air to the expansion tank to 17 PSI and adjusted the water feed to 17 PSI. Never had a problem.

    So read the I/O manual and adjust accordingly.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics