If it matters, I live in Ireland. We have an oil boiler powering a two zone hot water radiator heating system and a separate electric hot water tank for tap water.
Outside our house in the corner of our property we have a fenced in area. Inside that is a small metal box. I can remove one side of that box to access the boiler. When I look inside the box, up in one of the corners is this set of controls.
I assume the dial controls the temperature the boiler heats the water to, but what is the push button for? Please note, it is not the "reset" button, which is located on the boiler itself and glows red when the boiler pilot light is unlit.