I have a 1999 cal spa that when pump is running and jets are flowing, there is no heat and light is off. It all started when the spa said it over heated(OH) reading. Since then, pump is fine ,jets are flowing but no heat. Can anyone enlighten me on what and how to check this thing out.

Spa heaters include gas heaters for the swimming pool that are highly efficient. Every spa has a pump, a filter, and a heater of some sort. Electric heaters may vary in type and size. Heating your pool is an investment much deserved as it also enhances the value of your pool.