Need help with American Standard GPH Natural gas Boiler

jeffa_2

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 

neilc

show the compression or expansion tank also

jeffa_2

jeffa_2

I replaced the expansion tank with an extol #30

neilc

doesn't that front white cover lift off?
and there would be the aquastat under there,

EBEBRATT-Ed

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

Thanks, the only cover that comes off is at the bottom for the burner only, the rest is the jacket 

jeffa_2

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

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

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

Look under the white front cover or it may be behind a panel in the back or the
Nevermind!