How to Descale a Fire-Tube Steam Boiler

Fill the fire-tube boiler to the water line and close the steam stop valve on the steam line. Unscrew the safety valves on top of the boiler and set the valves aside. Turn off the boiler power switch.

Put on long-sleeved clothing, goggles and rubber gloves. Combine 1 pound of tri-sodium phosphate with 1 pound of caustic soda per 50 gallons of water.

Pour the chemical mix into the opening on top of the boiler and place an overflow pipe, included with the fire-tube steam boiler, on the safety valve opening. Turn the boiler back on and wait for the boiler to automatically refill with water.

Set the boiler to “Low” and keep it running for approximately four to five hours. Keep the temperature at the "Low" setting to avoid the production of steam pressure and monitor the overflow water in the overflow pipe during this time.

Stop the boiler once the water in the overflow pipe appears clear then wait for the boiler to cool to around 120 degrees Fahrenheit. Drain the boiler according to local regulations with regard to caustic soda and tri-sodium phosphate, two potentially hazardous chemicals.

Take out the hand and manhole plates from the boiler. Insert a hose nozzle into the boiler and wash the interior with regular tap water until the water that drains out appears clear.

Close all openings and safety valves then wait for the boiler to refill as normal. Turn on the thermostat until the boiler heats up to at least 180 degrees Fahrenheit. Discard any condensate and raw water so that corrosion or chemicals do not accumulate. Ask your local water treatment facility for regulations and recommendations regarding the disposal of condensate and raw water in your area as there may be specific regulations in place.