Explaining the Slow Low Water Cutoff Test

Take It Low and Slow

Explaining the Slow Low Water Cutoff Test

In a properly-working boiler, a low water level should trigger a shutdown of the burner system. That’s a good thing, because if your boiler keeps firing without enough water in it, it becomes an extreme risk to life and property. Checking your low-water cutoff regularly is extremely important. There are two ways to do it. 

To perform a standard low-water test, your boiler needs to be set at a reduced firing rate (50% or lower). Then, simply open the low-water cutoff blowdown valve and monitor the sight glass to make sure the water is draining rapidly. As the water level drops, the low-water cutoff safety should engage, and the burner should shut off. If it does, then simply close the valve and let the water level build back up until the burner restarts.

If your burner doesn’t shut off when you open the blowdown valve, or if it doesn’t restart when your water level returns to normal, contact our service department immediately. We’ll send a technician over right away to get you fixed up and operating safely. 

A more thorough way to test your water cutoff safety, though, is with a Slow Low Cutoff Test. This test better reflects the real-world conditions under which a cutoff safety would operate. To perform the test, your burner needs to be set at 50% or lower. Instead of opening the blowdown valve to force a rapid low-water situation, you are going to turn off the feedwater pump. Once the supply of feedwater stops, the boiler will begin converting all the remaining water to steam, and the water level will slowly drop since no feedwater is replenishing the boiler. 

Watch the water level at the sight glass. When the water level gets low, the burner should shut off. If during this test the water level falls below the level of the sight glass and the burner is still firing, your system has not passed the test. In this situation, you should immediately restart the feedwater pump, shut down the boiler, and contact WARE for an evaluation. Chances are, you either have:

  1. An improperly installed sight glass, or 
  2. A faulty low-water cutoff safety

Both situations can be remedied by our skilled service technicians. Remember, no matter what your boiler needs, WARE is standing by to help.

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WARE is an industrial & commercial boiler rental and service company that specializes in sales, service, valve repair, rentals, parts, turn key and boiler training.

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