Why Do Hot Runner Thermocouples Fail Easily?

Thermocouple failure is one of the most frequent issues in hot runner systems, often leading to production downtime and defective products. Common failures include open circuit, short circuit, reversed polarity, temperature drift, slow response, and physical damage. The main causes include improper installation, cable wear, high‑temperature oxidation, melt corrosion, mechanical vibration, and moisture ingress. Open circuits usually result from broken internal wires or loose terminals. Short circuits occur when insulation is damaged or molten plastic enters the sensor structure. Signal drift is caused by material aging, lack of calibration, or electromagnetic interference. Wrong polarity leads to abnormal temperature readings and system shutdown. Vibration during mold movement often breaks cable connections. Poor sealing allows moisture or plastic to penetrate, accelerating sensor failure. These problems increase maintenance time, raise production costs, and affect delivery schedules. This article summarizes the top ten failure modes, root causes, and on‑site judgment methods, providing practical solutions for technicians to quickly diagnose and resolve faults, reduce downtime, and ensure continuous and stable production.