Stack Temp Controller Usage Outfire?

Does anyone have experience with a stack temp controll device used as a out fire safety controller ?
I am reinsstallin a 53 520 and that controller is wired and I was trying to determine its function any one have ideas about it ?

I would guess, it prevents any continued coal feeding to a out-fire condition because it is only permitted if stack temp is above set point of controller.

There would need to be an *over-ride switch* of this stack temp controller for a period of time long enough to enable a normal cold start though.
Failure to *un-switch* or inadvertently switching anytime after sufficient stack temp would allow coal feed to an out-fire as if didn't have a controller.

If it were mine, I'd use a spring wound timer switch from Grainger as the *over-ride switch* for piece of mind.

The purpose of the aquastat is to shut down the stoker in the event of an outfire, so you don't end up with a base full of coal. As stated before, you do need to switch it off to start and establish your minimum boiler water temperature and then turn it back on for the protection. The wiring diagram is clearly shown in the 520 stoker manual at efmheating.com