The chemicals are used to keep various minerals in solution so that they don't coat the tubes and prevent heat transfer. Steam pressure is used twice daily to 'blow down' the boiler to flush out any suspended matter - again so that this doesn't settle onto the pipe surfaces. Every now and then (monthly?) they 'back-flush' the boiler system and pipe surfaces to remove any scale or build-up of insolubles to keep the heat transfer safe and effective. Once a year, someone gets inside the boiler and wire-brushes the pipe surfaces to keep them free of insoluble minerals.