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Radiators getting hot when only need hot water

I have an old boiler (oil hot water), domestic HW, radiators, and a RA89a transformer. With nothing being changed on the system, now when the system calls for hot water, the radiators get hot. I don't need heat, it's 70 degrees out. I just need hot water. Any help appreciated.


  • mattmia2
    mattmia2 Member Posts: 9,741
    edited September 2023
    Are the radiators steam or hot water? Show us a good picture of one or of the boiler if you don't know. We will probably need a good boiler picture capturing the controls and the piping anyhow.

    Edit, oh you said "oil hot water" so it is hot water.

    What @EBEBRATT-Ed said. Or possibly a stuck zone valve. Or a flow check valve that was manually opened during some sort of service and wasn't closed again.
    EBEBRATT-Ed Member Posts: 15,616
    If it is a hot water boiler you probably have a bad flow check valve.

    Need some pictures to be more specific.

  • fueloilrich631
    fueloilrich631 Member Posts: 16
    Just spitballing here based off of limited info provided, but it sounds like you have a bad flo-valve
  • ethicalpaul
    ethicalpaul Member Posts: 5,731
    Save yourself all this and install a standalone water heater and turn off your boiler in the summer.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el