To clean a cast iron boiler, a heating professional can:
- Use one pound of trisodium phosphate for every 50 gallons of water content.
- Fill, vent and circulate the system with above mixture, allowing it to reach design or operating temperature if possible.
- After circulating a few hours, drain the system completely and refill with fresh water. Usually, enough of the cleaner will adhere to the piping to give an alkaline solution satisfactory for operation: a pH reading between 7 and 8.5. Sodium carbonate (up to one pound for every 30 gallons of water content) or sodium hydroxide (lye) (up to one pound for every 50 gallons) may be used.
- Check pH level after cleaning. It should be between 7 and 8.5. A small amount of cleaner maybe added to adjust the pH up to the proper range.
- DO NOT use petroleum-based products in the boiler.