>>>Simply turn off the pump and all electricity going to the pool heater. Unbolt and remove the cover of the heater.Disconnect the wires from the old indoor gas shutoff switch.Remove the old gas shutoff switch by turning it counter-clockwise with a 11/16" open end wrench. Install the new gas shutoff switch, sealing it with a bead of RTV sealant before threading it into the exhaust elbow.Youtube videos are your best installation assistant- -- - /If you have any problems during guarantee period, please feel free to via YOUR ORDER/ / QA, We will reply to you within 24 hours. For whatever reason you are not satisfied, you can request >>>The pentair mastertemp 400 parts is an important safety component mainly used in pool and spa heater electrical systems.The switch monitors the temperature of the pentair pool heater and automatically turns off the gas supply when the temperature exceeds 135F, protecting the heater from high temperature damage. 42002-0025S and 42001-0063S have same 135F cutoff temp, VDC, and thread size. Replaces Part: 42001-0063S, STA-151-6255, 42001-0064S, HMXHLI2932, HAXHLI1930 >>>42001-0064S high limit switch is made of High-quality metal materials, resistant to corrosion and high temperatures.Replaces gas shutoff switch that has been damaged, corroded, rusted or failed. Each switch has undergone strict pre-factory testing, including pressure testing, temperature testing,air tightness testing, to ensure reliable operation under the most demanding conditions.Fix symptoms: Pool heater not running/AGS error code /Control panel showed HLS >>>The 42002-0025S Automatic Gas Shutoff Switch (AGS) compatible with Pentair Mastertemp (400 /200 /300/125) , Sta Rite Max-E-Therm (Sr200 / Sr333 / Sr400) Pool Heaters models, Sta Rite heater and all HD Versions, Mastertemp all the BTU's.Whether you're enjoying a leisurely swim or hosting a pool party, the AGS Switch ensures that your water remains at the ideal temperature, providing comfort and enjoyment year-round