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Hot water is suddenly hotter than usual- boiler

hockeyman70s Member Posts: 18
Hey all, this place is the best. I have an ancient (probably 40s boiler) that keeps on going. The last couple of days the faucets and shower in the house have been running noticeably hotter than usual. Wondering what may cause this? Thanks!


  • Jamie Hall
    Jamie Hall Member Posts: 23,640
    Two possibilities: the aquastat is not functioning properly or if there is a mixing valve, it's stuck.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
    Are you still using this dinosaur to make your hot water?

    I can't see the mixing valve in this photo so My guess is the Aquastat is calling for hotter water for some reason. Could be it is defective, or it could be an adjustment that was changed accidentally. I would guess the control on the water heater (Blue) is the reason, but without actually knowing how your mixture of mismatched parts is wired up it may also be from the other 2 controls (Yellow, Green) that have themperature adjustments therein.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • mattmia2
    mattmia2 Member Posts: 9,949
    If the boiler is warm start it could be a check valve is stuck open allowing gravity circulation too.