A steam boiler (Figure 5) would have a pressure control as a high-limit control, a low-water cutoff as a safety device, and a thermostat setting the comfort level. There will also be a rollout switch, ...

The first wiring diagram (Figure 7) is of a boiler with a float-type LWCO. A float-type LWCO has a three-position switch (Figure 8). When the boiler has enough water, the circuit between terminals 1 ...