Low Water Conditions: Possible Causes and Solving the Issue with Fuel Cutoff Devices

Low Water Conditions: Possible Causes and Solving the Issue with Fuel Cutoff Devices

April 22, 2022

These days boiler explosions are rare, but when they occur, they usually make the day’s headlines.

The explosive force of even a small boiler can cause catastrophic damage to the equipment, but also neighboring rooms, buildings, and even personnel.

Typical causes for such events include a stuck safety valve or poor water treatment which leads to scaling and overheating of the metal. A third cause, which is easily preventable, is low water level.

What causes a low-water condition?

  • Someone left the boiler blowdown valve partially open.
  • The relief valve or safety valve has discharged.
  • The condensate pump or feedwater pump isn’t working as it should.
    • The float may have come loose.
    • The condensate may be too hot to pump. (Check those steam traps!)
  • Heavy deposits (scale) on the waterside surfaces.
    • Check the pH of the water. It should be between 7 and 9.
    • Check the condition of the water.
    • Check the burner’s firing rate.
  • All of the condensate may not be returning from the system (a common problem with process applications).
  • Loss of plant compressed air pressure to the control valve actuator, if applicable.
  • Large sudden changes in steam load.
  • Improper wiring of low water cut off devices.

To avoid a boiler explosion or damage from loss of water, a low water fuel cutoff device should be used. Such a device will shut down the system by turning off electrical current to the firing device, should the water level system fall below a safe level.

There are two main types of low water fuel cutoff devices: Electronic devices, which use a probe; and mechanical devices, which use a float switch. Both variants are also available combined with pump controllers.

Most boiler systems have a secondary or back-up cutoff, which is typically a probe type with a manual reset. Your American Boiler & Mechanical technician can make sure you’re using the best device for your situation.

Testing the Cutoff

Regular testing of your cutoff is recommended. There are two ways to test: The Quick Drain Test, which focuses on the float within the cutoff; and the more involved Slow Drain Test, which requires lowering the water in the boiler. Your American Boiler & Mechanical technician can walk you through these tests to ensure system safety and operability.