Stack Flue Sensor Replacement for Pentair/Sta-Rite - Replaces 42002-0024S Replaces Pentair/Sta-Rite 42002-0024S Typical Error Codes: E-05, E-06 These error codes usually mean that the stack flue sensor needs to be replaced. Location: The Indoor Stack Flue Switch (ES2) / Stack Flue Sensor (SFS) is located on the exhaust Elbow. Function: The Stack Flue Sensor prevents the flue gas output from exceeding 500 degrees F +/-18 degrees F. Turn off the filter pump and all electrical power to the pool heater. Allow the heater to cool for at least 30 minutes before proceeding to the next step. Unbolt and remove both the upper left and upper right jackets from the heater. Disconnect the wires from the old indoor stack flue sensor. Remove the old sensor by turning it counter-clockwise with a  open end wrench. Install the new sensor, sealing it with a bead of RTV sealant before threading it into the exhaust elbow.