This could be caused by a faulty part like a failed heater, circulation pump or thermostat, or even simply that there is not enough water in the hot tub. Dirty Filters can also cause a tub to stop heating - If a filter becomes too dirty it can prevent your hot tub from properly circulating and heating itself. This can also lead to reduction in jet pressure. Rinsing filters monthly and soaking them in Filter Cleaner every 3-4 months prevents most problems. If your hot tub is unable to run and heat itself you may be forced to remove your filters until they can be properly cleaned or replaced. After removing your filters turn off power to spa for 30 seconds, then restore power and allow the spa several hours to reheat. If the spa still does not function properly contact us for service.