My Cal Spa will not start (possibly following a close lighting strike) I get a "Sn" display reading but tub will not turn on. Any suggested diagnostics I can do?
You can try unplugging the spa sensor (http://www.hottubworks.com/SpaParts/HeaterSensors.php) harness, wait a few moments and then plug back in. You would want to turn the power off before doing this. Usually a SN error code is signaling that one of the sensors is failing, but since you said that it was a possible lighting strike then your circuit board (http://www.hottubworks.com/SpaParts/ElectricalCircuitBoards.php) could have been damaged.