Intermatic 156T4042A Fireman Switch Kit Control For any Pool/Spa Heater and Filter PumpThe 156T4042A Fireman Switch provides coordinated control for any pool/spa heater and filter pump. It is designed to turn OFF a gas fired pool/spa heater approximately 20 minutes before the filter pump shuts down. This eliminates the problem of pounding and knocking caused by overheated water and also reduces scale and lime deposits and extends service life of the heater.