Notwithstanding the prohibition contained in Section 25960, any swimming pool heater with a pilot light which was manufactured prior to February 24, 1984, and in stock or on order as of that date, may be sold in this state prior to December 1, 1984. On or after December 1, 1984, no swimming pool heater may be sold or offered for sale, unless it is equipped with an intermittent ignition device or is designed to burn only liquefied petroleum gases.