Click here to Find a Contractor in your area.
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/.

High pressure on hot water boiler

michael123
michael123 Member Posts: 5
Hello. I have a Laars JVS hot water boiler with cast iron radiators. It was installed about 3 years ago. When it runs and the temperature rises, the pressure rises and hits 30 PSI. The pressure reducing valve is working and expansion tank is not leaking water. About half of the tank is water and half air.
The bypass valve was half sized so the plumber put in full size bypass near the boiler. What got me thinking is that maybe the bypass is supposed to be after the expansion tank and pressure reducing valve. Currently it’s right next to the boiler.
Please see the picture attached. It shows the old bypass and the new bypass. The second picture shows the pressure reducing valve and expansion tank.



Comments

  • Jamie Hall
    Jamie Hall Member Posts: 16,593
    Well, the expansion tank and all may or may not be in the right place, but...

    If the pressure rises that much, the expansion tank simply isn't doing its job. Assuming that it isn't actually somehow valved off from the system, either it's failed, it's too small, or it wasn't pressurized properly (or has lost its pressure -- same thing as failed). Unhappily, I don't see any good way to isolate the tank from the system and drain it -- which is the only correct way to set its operating pressure.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,678
    What @Jamie Hall

    said. Expansion tank likely failed
  • JUGHNE
    JUGHNE Member Posts: 8,680
    edited March 1
    If you press the air valve on the bottom of the tank what comes out?
    If water....tank is bad. If some air, it might needing topping off.
    With system cold, tank should be empty. As the water expands it will push itself into the tank.


    What is the cold pressure on the system?
    The tank should be set at 12-15 PSI when it is not connected to the system.

    Also, if you have cast iron radiators and what looks to be large piping in the basement, that tank may be borderline for size. Air tank size is based on the water content of the system.
    You may need the next size up for tank.

    Is there only one pump on your system?
    Is that bypass valve always fully open?
    SuperTech
  • michael123
    michael123 Member Posts: 5
    Hi. If I press the air valve on the tank, only air comes out, no water. When the boiler has been off for a while, the pressure is about 15psi. 
    Yes, there is only one pump and the bypass valve is fully open.
  • Jamie Hall
    Jamie Hall Member Posts: 16,593

    Hi. If I press the air valve on the tank, only air comes out, no water. When the boiler has been off for a while, the pressure is about 15psi. 
    Yes, there is only one pump and the bypass valve is fully open.

    15 psi in the system? Or in the tank. Check the tank air pressure with a reliable tire gauge -- although that won't tell you if it was properly precharged.

    And I tend to agree with the folks above -- that tank looks pretty small for a system with pipes that size.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • The expansion tank is screwed into a black tee, the perfect place for sediment to build up. I would remove the tank and stick a long screwdriver up through the tee and into the microbubble air eliminator to make sure it's all clear.

    When you replace the expansion tank, add a ball valve so that you don't have to drain the entire system to service the tank.
    Often wrong, never in doubt.
  • bucksnort
    bucksnort Member Posts: 112
    A bigger tank might not fit with that lower bypass setup as is. My new system going in this Summer is on the borderline on needing a 60 instead of a 30. The old bladderless tank is in good shape and i might just keep it. But I'll make provisions to easily add a 60 should the bladderless decide to sheit the bed down the line.
  • JUGHNE
    JUGHNE Member Posts: 8,680
    A larger tank can be piped with fittings to a different location.
    IDK about the 60, but the 90 has a 3/8" female spud on the bottom.
    I used it to provide floor support with 3/8" all thread rod.
  • bucksnort
    bucksnort Member Posts: 112
    edited March 1
    JUGHNE said:

    A larger tank can be piped with fittings to a different location.
    IDK about the 60, but the 90 has a 3/8" female spud on the bottom.
    I used it to provide floor support with 3/8" all thread rod.

    I agree 100%. But looking at the pics a new 60 wouldn't be a simple spin and replace with those existing pipes in the way. OP still needs to verify if there's even air pressure in the tank now and then go from there. Spinning on a new 30 might be a quick fix until he can repipe.
    Just looking at the pics it looks like big supply and return pipes. Only after adding it all up can a choice be made. It never hurts to go bigger on a tank.
  • JUGHNE
    JUGHNE Member Posts: 8,680
    He mentioned cast iron radiators, looks like an old gravity system.
    If a 30 made it for 3 years, a 60 would not be overworked like the 30 might have been.
  • michael123
    michael123 Member Posts: 5
    Hello. Thank you all for your response. My boiler output is 63k Btus. My average pipe size is about 1.9 inch. The supply side length of pipe along the wall is about 46 feet and the same for return. The unit is in the basement and only heats the first floor radiators. 
    I don’t know the current pressure as I don’t have a gauge but the factory install pressure was 12 psi.  
  • dopey27177
    dopey27177 Member Posts: 717
    Here is a possibility.
    The cold pressure on the system should only be 2 psi above the static head of the system pressure,
    Assume you are in a building where the the highest radiator or convector is 10 feet above the radiator the static pressure is 10 X .434, that means the the static head is 4.34 psi add 4 psi that that number and you will have 8.34 psi cold pressure. when the water heats up the pressure will go up.
    If the pressure goes up to 30 ten the compression tank is to small.

    I am a little dopey here what are the by passes for. Me thinks both bypasses should be closed when you re in the heating mode.

    Jake
  • Henry
    Henry Member Posts: 988
    The proper way to check the tank is to remove it. Then check the pressure of the tank. Pump it to operating pressure. Wait 30 minutes and then check the air pressure in the tank. You will be surprised that it has probably not dropped. I have seen in 44 years very very few tanks that have failed. The tanks loose 4% of the air through the bladder. It is a great $$$ for an inexperienced plumber or a scammer to replace commercial expansion tanks without a proper test. I saw one replaced with an ASME 150 gallon expansion tank for a four floor 32 apartment building last week. A PX 90 would of done the job.