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Need help with American Standard GPH Natural gas Boiler

jeffa_2
jeffa_2 Member Posts: 8
I’m stumped, I’m looking at a 50 year old American Standard Natural gas Boiler model GPH-100. The boiler is operating between 180*F and 220*F. And due to the overheating the pressure is approaching 30PSI causing the relief valve to drip. 
I cannot find a high & Low limit control anywhere, I’m puzzled. 
Does anyone know what controls the high and low limit on this boiler? 
I will send pictures 

Comments

  • neilc
    neilc Member Posts: 2,016
    show the compression or expansion tank also
    known to beat dead horses
  • jeffa_2
    jeffa_2 Member Posts: 8

  • jeffa_2
    jeffa_2 Member Posts: 8
    I replaced the expansion tank with an extol #30
  • neilc
    neilc Member Posts: 2,016
    doesn't that front white cover lift off?
    and there would be the aquastat under there,
    known to beat dead horses
    bburd
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,654
    There has to be a high limit there somewhere or the boiler would have cooked long before this. look inside the jacket cover
  • jeffa_2
    jeffa_2 Member Posts: 8
    Thanks, the only cover that comes off is at the bottom for the burner only, the rest is the jacket 
  • jeffa_2
    jeffa_2 Member Posts: 8
    I agree there has to be a high limit somewhere maybe it is built in under the jacket but I’ve never seen that before 
  • mattmia2
    mattmia2 Member Posts: 6,655
    Where does the thermoplastic wire from the R845a low energy contacts go? The limit aquastat has to be between that and the burner.

    Also, what is that toggle switch on the junction box? Does it permanently turn the circulator on or off?
    jeffa_2
  • jeffa_2
    jeffa_2 Member Posts: 8
    Thank you for the hints! I found it in the junction box where the toggle switch and the transformer mount. However, there is no adjustment, it must be factory set. I think the only fix now would be to install a new strap on Aquastat to interrupt power to the gas valve at 180*F 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,271
    edited November 23
    Look under the white front cover or it may be behind a panel in the back or the
    Nevermind!
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org