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Radiant in floor system over pressure

ebm
ebm Member Posts: 5
in Radiant Heating
My infloor system was installed about 13 years ago by an infloor engineer. The company subsequently closed. After a couple of years the system started to blow off. I purchase “pumping away” and discovered that the pump was pumping to the expansion tank. I had my plumbing and heating guys change the pump and tank location but the system continued to blow off. I also purchased Primary/Secondary pumping and had the system set up accordingly but the blow off continued. We increased the size of the expansion tank and that didn’t work so my plumbing guys and I are at a loss to solve the problem. Any ideas?

thanks

Dave

Comments

  • Zman
    Zman Member Posts: 7,611
    edited September 2021
    Under what conditions does the pressure rise? Does the gauge show the temp rising to the relief valve's rated pressure?
    Could be:
    • Bad relief valve
    • Bad fill valve (or improperly located)
    • Improper expansion tank pressure (needs to be charged to system pressure when isolated from system)
    • Pinhole in indirect heat exchanger
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Solid_Fuel_ManIronmanSTEVEusaPA
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    I agree with @Zman. My first question was how are you heating your domestic hot water? 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • ebm
    ebm Member Posts: 5
    The heater is a Slantfin Molitron electric boiler. The temp gauge shows both the temp (120 - 130) and the pressure 27 to 30 psi where it starts to drip fluid. The pressure valve and the fill valve have both  been replaced twice. The reduction valve coming into the house has been replaced. The domestic hot water is on a separate system with its own 60 gal electric hot water tank. The floor system has its own 60 storage tank because we are on a time of day power set up 
  • Ironman
    Ironman Member Posts: 7,550
    What size is expansion tank? You may need a larger one with that 60 gallon storage tank.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • ebm
    ebm Member Posts: 5
    The expansion tank is a Watts ETX 60
  • Ironman
    Ironman Member Posts: 7,550
    Also, was the air charge adjusted to match the pressure setting of the fill valve before it was connected to the system?
    The tanks normally come precharged to 12 psi, but if the fill valve is set higher, the the air charge needs to be increased to match that or else the tank’s capacity is decreased.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Zman
    Zman Member Posts: 7,611
    What is your design pressure? The pressure the fill valve and tank are set to. Does the pressure rise consistently as the system heats up?
    Can you post a picture that shows the orientation of the circulator, expansion tank, and fill valve?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jamie Hall
    Jamie Hall Member Posts: 24,857
    I think -- but I'm not positive -- that your problem is that the expansion tank is much too small. It would be about right for the radiation -- there's a fair amount of slack in there in the sizing -- but you have that 60 gallon storage tank. Look at it this way. That tank is, as I say, sized more or less right for a typical hot water heating system. Such a typical system will have around 20 gallons of water in it. You have that expansion tank, so your system has a water volume four times that. That's just not going to work...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ebm
    ebm Member Posts: 5
    Thanks to all for the responses. First to Ironman,I believe the tank was pressurized to 15 psi to be the same as the fill valve.
    second to Zman the system is set up for 15 psi and yes the pressure does slowly rise as to heats up.
    thirdly to Mr Hall, My plumbing guy was thinking the same thing. I don’t have room in my mechanical room for a floor tank so he is going to tee in another ext 60. Hopefully that solves the issue. Thanks 
  • ebm
    ebm Member Posts: 5

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