Replacement Stack Flue Sensor — Part 420020024S Key benefits Prevents dangerous flue overheating by stopping flue gas output from exceeding 500°F, protecting your heater and surrounding equipment. Restores proper operation and clears common fault codes (E02, E05, E06), reducing downtime and service calls. Directfit replacement for affected Pentair electrical systems — avoids modification and simplifies installation. What this part does Monitors flue temperature and signals the heater control to limit or shut down combustion if the flue exceeds safe limits. Operating temperature range: 20°C to 105°C (see product listing images for exact appearance and mounting). Designed to correct error conditions commonly associated with a failed or outofspec flue sensor (E02, E05, E06). Compatibility (do not unless your model matches) Replacement Part Number: 420020024S Fits Pentair MasterTemp pool and spa heater electrical systems Also fits Pentair StaRite MaxETherm pool and spa heater electrical systems — models SR200, SR333, SR400 Performance and reliability Keeps flue gas temperature within safe operating limits (prevents exceedance above 500°F). Intended to heaters to normal operation when the original flue sensor is faulty or out of tolerance. Use as a direct replacement to maintain correct safety controls on the listed Pentair/StaRite systems. Practical use scenarios a failed flue sensor on a Pentair MasterTemp heater to clear recurring E02/E05/E06 errors and restore heat production. Install during seasonal maintenance when diagnostics show abnormal flue temperatures or intermittent shutdowns. Use as a service replacement in a pool equipment handling Pentair MasterTemp or StaRite MaxETherm (SR200, SR333, SR400) units. Installation notes and tips Confirm your heater model and electrical system match the compatibility list before . Review the product images and your heater's wiring/connector details to ensure proper fit. If you are not comfortable working with gasfired heaters or electrical systems, have a qualified technician perform the replacement. Important: Carefully read the full page description and inspect the reference images to verify fit and compatibility with your specific unit before ordering.