Blow down your steam boiler.

All steam boiler manufacturers recommend that the low water cut out be "blown down weekly." How to blow down? When the boiler is steaming (up to operating pressure and temperature) the valve located at the bottom of the low water cut out is opened for 5-7 seconds. With the boiler firing, and the blow down valve open, the burner shuts off and will restart when blow down valve is closed. This verifies safe and correct low water cut out operation and keeps the assembly free of scale and debris. DANGER: THE DISCHARGE WATER TEMPERATURE WILL BE 200 DEGREES F AND CAN CAUSE SEVERE BURNS OR DEATH. USE PROPER PRECAUTIONS. Denver Building code states that the water temperature discharged into the sanitary sewer must not exceed 180 degrees F.