Boiler drainage is to blow down a portion of the high condensed water, in order to fill in fresh water to maintain the water quality in the boiler body. Since the concentration of water can be different according to the change of the blow down cycle, the technician can periodically collect and test the boiler water, and blow down the water when needed.

Normally, a good drainage cycle for the boiler is around every 8 hours of operation, one full drain. If the boiler only works 4 to 5 hours a day, then the full drain can be done once every two days.