Pentair Stack Flue Sensor for Max-E-Therm and MasterTemp Heater Electrical System 42002-0024S
$199.99
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Pentair Stack Flue Sensor for Max-E-Therm and MasterTemp Heater Electrical System 42002-0024S
$199.99
The Pentair 42002-0024S is the official replacement Stack Flue Sensor (SFS) used in Pentair MasterTemp (including MasterTemp 125, 200, 333, and 400) and Sta-Rite Max-E-Therm gas pool and spa heaters.
It acts as a safety mechanism located on the heater's exhaust elbow, monitoring combustion exhaust temperatures to prevent the internal system from exceeding 500°F.
Common Signs of Failure
- E05 or E06 Error Codes: The most distinct sign of a bad sensor is an active E05 (Stack Flue Sensor Fault) or E06 error code on your heater's digital display board, which automatically shuts down the system for safety.
- Resistance Testing: You can verify if the sensor is bad using an ohm meter. A functioning sensor should read between 3.5 to 4.0 megaohms of resistance. If it reads completely open or sits outside this threshold, it needs to be replaced.
- Root Causes: If you swap the sensor and it fails again quickly, your heater may actually be overheating. This is frequently driven by internal calcium scale buildup in the heat exchanger or poor water circulation.
How to Replace It
Replacing this sensor is a straightforward, drop-in repair that requires a ½-inch open-end wrench.
- Cut the power: Turn off the filtration pump and completely disconnect the electrical power to the pool heater.
- Cool down: Let the unit cool for at least 30 minutes.
- Open the casing: Remove the upper jacket panels from the heater body to expose the internal wiring harness.
- Swap the hardware: Disconnect the two red wire leads. Use your wrench to unscrew the old sensor counter-clockwise from the exhaust elbow.
- Seal & install: Thread the new sensor in clockwise. It is highly recommended to apply a small bead of high-temperature RTV silicone sealant to the threads before installation to ensure a proper seal. Plug the wire leads back into the harness.