Turn your boiler off and wait for it to cool down. Examine the back of the boiler to find the device's information sticker.
Record your boiler's serial number. To determine the age of your boiler, look at the numbers after the serial number's dash. If the number ends in a four-digit code, then the boiler was made before the year 2000 with the last two numbers of the code indicating the exact year the boiler was made. If the number ends in a six-digit code, the boiler was made after the year 2000 and the last three to four numbers indicate the month and year the boiler was made.
Turn your boiler back on and keep your serial number recorded in an easily accessible location.