I know we hear these words frequently, and I will agree that safety is a good motto to live by. There are many safety devices, the oil safety valves, thermal-fire-o-matic oil valves, and many more available, but one that is often misunderstood is the low water cut off valve.
It, too, is one of the most critical safety devices on the heating system. Once, we only heard about this unit when we heard about steam boiler applications. However, some states have now made it a requirement to have a LWCO (safety device) installed on hot water boilers as well. I believe that every state should have this policy and boiler manufacturers should consider it a standard practice to install the unit at the OEM level. I know that cost is often a factor when making these suggestions.
Many of you, I’m sure, are familiar with the older combo units found on the steam boilers, like the 47-2 combo feed and cut off unit. When this unit senses the need for more water, the mechanical float will open a valve and allow the water to feed into the boiler until it reaches the proper level in the gauge glass. This level is determined by the manufacturer’s location of the gauge glass connections and the steam chest. (Traditionally, a proper level is slightly over half of the gauge glass.)
On the other hand, if the water level drops below the predetermined level, the float will then trip the internal electrical switch that will interrupt the power to the burner. The No. 67 LWCO is often married to a No. 101 feeder. These two separate units, unlike the 47-2, are connected together electrically. In the case of these units, when the water level drops, the power to the burner will be cut off, but the 101 feeder will continue to function until the proper water level has been restored. At this time, the power to the burner will be restored and the feeder will stop feeding water to the system upon reaching the proper level.
Many of you will say, and I will agree, the major problem with these devices is lack of maintenance. Often we have found floats jammed with rust accumulation that has caused the float to stick and giving a false signal, allowing the burner to run with no water in the boiler. Think also of the times you have seen a boiler glowing red and cracking. Again, no water!
When you take a float type device out of the box, you will notice a small tag attached to the unit. Read this tag carefully as it will say ‘Flush the unit weekly during the heating season.” Make sure that the homeowner or the commercial building manager is aware of this requirement. I have heard of insurance claims being rejected because of the lack of maintaining these units, which means flushing them.
Today, we have more advanced electronic probe-type feeds and low water devices that have dip switches to set the amount of water feeding and when, in order to avoid flooding the system, often caused by slow returns. There are also units that provide for boiler water temperature control and low water protection all in one control. Now several companies are installing an electronic controlling unit on every boiler regardless of whether it is water or steam or determined by law. On a final note, be sure to read the instructions that come with the carefully selected unit to become familiar with the servicing required. Erring on the side of safety is a must.