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.