The Pentair Stack Flue Sensor (42002-0024S) is the OEM replacement exhaust temperature sensor for select Pentair MasterTemp and Sta-Rite Max-E-Therm pool heaters. If your heater is shutting down unexpectedly, displaying a flue-related fault, or failing to complete ignition, this sensor is a common service component to inspect and replace. ⚠️ IMPORTANT: NOT COMPATIBLE WITH MASTERTEMP 125 This sensor does not fit the MasterTemp 125 heater. MasterTemp 125 owners require a different sensor part number. Always verify your heater's model number and confirm the part number against your equipment's parts diagram before ordering. ⚠️ IMPORTANT: PROFESSIONAL SERVICE REQUIRED Gas and electrical heater components must be serviced by a licensed pool professional or qualified HVAC technician. Do not attempt to service gas or high-voltage components without proper certification and in accordance with local codes and the manufacturer's installation manual. The stack flue sensor monitors exhaust gas temperature at the flue outlet. When flue temperatures exceed a safe operating threshold — which can result from venting or airflow restriction, sooting, scaling, improper combustion, or related component faults — the sensor interrupts the circuit and triggers a safety shutdown, protecting the heat exchanger and surrounding components from damage. A faulty sensor or degraded wiring can also contribute to nuisance shutdowns, fault indications, or ignition lockouts even when the heater is otherwise serviceable. Specifications Pentair Part Number 42002-0024S Part Type Stack Flue Sensor Part Category Sensors Quantity Included 1 (Each) Fits Into Brand Equipment Line Model / Part Number Notes Pentair MasterTemp Heater MasterTemp 175 / 200 / 250 / 300 / 400 Verify against your heater's parts diagram. Does not fit MasterTemp 125. Pentair (formerly Sta-Rite) Max-E-Therm Heater — Max-E-Therm Series MAX-E-THERM — Pentair Heater Master Kit — All / MasterTemp / Max-E-Therm Series 461100, 461101 This sensor is included in Heater Master Kit - All (461100) and Heater Master Kit - Electrical (461101). Order this standalone listing if you need the sensor only. Compatibility is based on Pentair parts documentation and available OEM records. This is not an exhaustive list. For certainty, verify the part number in your equipment's manual or on the original part itself before ordering. Pro Tip Before ordering, locate the existing sensor in your heater's flue outlet area and confirm the part number printed or stamped on the sensor body matches 42002-0024S. MasterTemp and Max-E-Therm heaters have used multiple sensor part numbers across production revisions — matching the number on the original part is the most reliable verification method. If your heater is displaying a flue-related fault code, also inspect the sensor wiring and connector for corrosion or heat damage before replacing the sensor itself.
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