1472 = days of service between FRA complete inspection. The regulation is 15 years or 1472 service days (whichever comes first) between these complete boiler inspection which includes removal of flues, etc.
As I understand it a service day is any day with a fire in the firebox.
There are other lesser required inspections that occur on a calendar basis of 30 days, 90 days, annual. But the big one is the 15 year or 1472 days. The old ICC regulations required a complete inspection every 36 months; and a month was any month with even one service day.
Brian Norden