Weil McLain 381-356-577 Temperature Sensor

Keep your heating systems running at peak performance with the genuine Weil McLain 381-356-577 Temperature Sensor. Designed specifically as a boiler supply temperature sensor, this 12K ohm NTC thermistor provides critical feedback to the control module, ensuring high-accuracy water trim monitoring and safe operation. This direct-replacement component features a 1/2" NPT threaded connection, making it compatible with a wide range of popular hydronic units including Weil McLain CGa Series 1 & 2, CGi Series 2 & 3, and GV90+ Series 2 gas boilers.

For a veteran contractor, this is a standard truck-stock item for troubleshooting thermal fluctuations or low water cutoff (LWCO) sensor errors. This high-precision NTC 12K ohm sensor operates with an inverse resistance profile—as temperature increases, resistance drops—allowing the boiler’s control logic to modulate firing rates and maintain supply water setpoints without short-cycling. The 381-356-577 is engineered to withstand the demanding environment of modern hydronic loops, offering reliable 1/2" NPT boiler sensor integration for both residential and light commercial service calls.

• Exact OEM Calibration: Pre-calibrated 12K ohm resistance curve ensures perfect communication with Weil McLain ignition control modules.
• Broad Compatibility: Suitable for widespread models like the CGa, CGi, and GV90+, reducing the need for multiple SKUs.
• Direct Mechanical Fit: Standard 1/2" NPT connection provides a secure, leak-free seal in the supply manifold or water trim location.
• System Efficiency: Accurate thermal sensing allows for proper modulation, supporting outdoor reset control kits and reducing fuel consumption.

How do I test a Weil McLain 12k ohm sensor?
Using a high-quality multimeter set to ohms, disconnect the wire leads and measure the resistance across the sensor terminals. At approximately 77°F (25°C), the sensor should read 12,000 ohms. Significant deviation commonly indicates a failed element.

Will this sensor resolve "flashing light" error codes on the control module?
If your diagnostic guide points to a Water Temperature/LWCO sensor malfunction or an open/shorted sensor circuit, replacing the 381-356-577 is the standard procedure to restore ignition sequence.

Can this be used for both supply and return lines?
This specific part number is primarily listed as a supply water temperature sensor for compatibility with CGi and CGa series logic controllers. Always verify your specific model's wiring schematic for correct placement.

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Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.