My heater isn working. What is the problem?
Pool and spa heaters are different. Pool heaters have a pressure switch that will stop the heater if there’s not enough water flow to cool the heater and prevent cracking. Spa heaters don’t usually run as hot, and they have a different mechanism for shutting off if there is poor flow from a filter being too dirty. In both cases, cleaning the filter (sometimes just backwashing or changing the cartridge) will do it).
