To find your boiler's age you need a couple of pieces of information. The first is boiler's (ie unique) serial number. (Sometimes this is only inside but is often on a label on the case somewhere).

 

Once you have that serial number, (other than Worcester which are needlessly secretive - call them on 0330 123 9559!) look at the example serial number below and find in the format example yy (year) and likely  ww(week number - eg 07 is seventh week - ie in Feb)  or mm month, dd day

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Baxi                                   ABCyyww89123XY

Ideal Logic                       AB 12243134431432  5424  yy/mm/dd   - ie the actual date in American format

Glowworm or Vaillant:   20yyww4321414343243432....

Viessmann    a 16 digit number , best decoded on the Viessmann website

Potterton changed formats many times  - for them and others - call the manufacturer's service number