unless there is a way to prove there is water inside the boiler. For hot water boilers there are different components for this and we will discuss it later but for steam boilers should have a way to automatically feed water to the system and to shut down the ignition controls when and if the water inside the boiler reaches a predetermined and unsafe level. Most low water cut-offs work as a float type of switch where the float is set to a water level minimum and when the water falls below this level the steam boiler is prevented from firing. Of course the job of the automatic water feeder will be to keep the water level above that safety level point but if something would happen to the automatic water feeder to where it stops delivery make-up water to the boiler then the low water cut-off would save the day and shut the boiler down. Another good reason to blow your steam boiler down at least once a month to keep fresh water in the system. This drains the foul water and keeps it from fouling the low water cut-off float and the automatic water feeder. It also allows you to hear the automatic water feeder feeding fresh water into the system.
Residential Hot Water Boiler Control | HVAC Heating – Flow Switches for Hot Water Boilers
Some boilers have a different method of determining there is water in the boiler and this method is either a flow switch or a low water cut-off. And yes there are some boilers that do not have any way to determine if the boiler has water in it before the boiler can fire. Those boilers have been tested by the manufacturer to not require low water cut-offs. However, boilers that do have flow switches ensure the boiler will not fire unless flow is determined by the flow switch. The flow switch is usually integrated with the safety circuit and if the safety circuit is open the boiler will not fire.
Residential Hot Water Boiler Control | HVAC Heating