Weil McLain 383-500-300 Sensor

The Weil McLain 383-500-300 is an OEM-spec Return/Supply Water Sensor designed for precision temperature regulation within hydronic systems. Engineers and technicians primarily utilize this 12k ohm NTC thermistor kit for Weil McLain Ultra Series boilers, specifically supporting Ultra Gas Boiler models such as the Ultra 310 and Ultra 80 (Series 1 & 2). By delivering real-time data to the U-Control module, it allows the unit to modulate firing rates based on accurate supply and return water temperature differentials, preventing thermal shock and short-cycling.

Replacing a failing water temperature sensor is critical for maintaining high-efficiency combustion and delta-T requirements. This kit provides an exact-fit replacement that eliminates common boiler error codes associated with inaccurate resistance readings. Field professionals rely on this 383-500-300 sensor kit for its durable construction and seamless boiler control board integration, ensuring the hydronic heating system operates within the manufacturer's specified thermal parameters without nuisance lockouts.

• Precise Modulation: Provides accurate feedback to the U-Control for optimized fuel-to-air ratios and temperature stability.
• OEM Compatibility: Engineered specifically for Weil McLain Ultra Gas units, ensuring electrical and physical fitment.
• System Protection: Monitors return/supply differentials to protect the heat exchanger from rapid temperature fluctuations.
• Critical Replacement: Resolves sensor drift or failure that causes inconsistent boiler cycling and decreased efficiency.

What resistance should I see on the 383-500-300 sensor?
This is typically a 12k ohm NTC thermistor; verify resistance values against the Weil McLain temperature/resistance chart found in the boiler service manual for diagnosis.

Can I use this on different Ultra boiler sizes?
While commonly cited for Ultra 310 and Ultra 80 Series 1-2 models, always check your specific unit serial number and parts list to confirm compatibility before installation.

Does this kit include the mounting hardware?
The kit includes the primary supply/return sensor assembly. Secondary items like specialized sensor wells or bulb retaining springs (e.g., part 383-500-305) may be required depending on the application.

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.