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Should radiant heating boiler consume water?

alex2022 Member Posts: 3

I am a complete newbie in radiant heating, so sorry for a stupid question.

I live in an Eichler home with functioning radiant heating (60yo pipes in concrete foundation, relatively new Prestige Solo boiler)

I noticed that every time the heating is on, boiler pulls water from the line (can hear and see it on the gauge). Does it mix water in the heating pipes with fresh water or always circulates fresh water? Shouldn't it always re-circulate existing water so it's easier to heat it up and avoid extra water consumption?

Thank you.


  • GGross
    GGross Member Posts: 976

    No, a properly functioning radiant heating system will be a closed loop that circulates the same heating fluid. there are sometimes filling units attached to the system, so that in the case of a leak you may fill the system back to the correct pressure, I like to leave those closed off so that everyone knows if there is a leak as it needs to be fixed. Can you post some pictures of your setup, and perhaps show us where the connection to fresh water is made with your system?

  • hot_rod
    hot_rod Member Posts: 21,882

    the system should hold pressure, always. A 60 year old steel or copper tube system could be on borrowed time 🧐

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606

    If it is consuming water on a regular basis, then you have a leak. How do you know it is consuming water? Think of it like a bottle of water with some lengts of tubing that are making a circle outside the bottle with one end connected to the top and the other end connected to the bottom. They would be the pipes to the radiators and back. If the connections to the bottle are not leaking then the water can never leave. If the bottle and pipes are full, and water never leaves, there will be no room to add water.

    So if there is room to add water… there is a leak

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • jumper
    jumper Member Posts: 2,208

    Some servicefolk are convinced that radiators somehow evaporate some water. Then there's the theory that pump seal lets air in & water out?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606

    AND I STILL BELIEVE THE EARTH IS FLAT AND IS THE CENTER OF THE UNIVERSE. There is a large group of us all around the globe that agree with me!

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics