The 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.

Intermatic® Heater Control/Fireman Switch Kit, 250 VAC, 10 A, 60 Hz, For Use With: Pool/Spa Heater and Filter Pump, Metal

• Coordinated control for pool/spa heaters and filter pumps
• Turns off gas pool/spa heater before filter pump shuts down to extend heater life
• 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
• Reduces scale and lime deposits, extends the heater service life, eliminates pounding and knocking caused by overheated water

• Instruction/Installation Manual https://assets.unilogcorp.com/2/ITEM/DOC/Intermatic_156T4042A_Installation_Instructions.pdf