Aquarite has a warranty that is Ebay friendly. At a minimum their 5 warranty is based on date of manufacture, even if you don't have a receipt, etc.

If written proof of the date of the initial system installation is not provided to Goldline, the manufacturing datecode on the Aqua Rite, Aqua Trol, or Aqua Logic electronics unit will be the sole determinant of the date of the initial system installation.
http://www.goldlinecontrols.com/Warranty.aspx

Is this standard for the SWG industry?