Hot Runner Heaters & Thermocouple Maintenance Guide

Hot runner systems are a crucial component of the injection molding process, and ensuring their efficient operation is vital for maintaining production quality and minimizing downtime. Hot runner heaters are one such component that requires regular maintenance to prevent failures and ensure optimal performance.

Typically, 80% of our customers are weakest in their electrical skills and understanding how thermocouples and heaters actually work, and what to test for. In this article, we will discuss some essential tips for maintaining hot runner heaters and thermocouples.

Regular Maintenance Schedule

Firstly, it is essential to have a maintenance program in place for hot runner heaters. This program should include a regular inspection of the heaters, checking for any signs of wear, damage or discoloration, which may indicate a need for repair or replacement. Additionally, it is recommended to test the heaters periodically to ensure they are heating correctly and consistently. It is also important to keep track of the maintenance schedule.

Hot Runner System Cleaning

Secondly, proper cleaning of the hot runner system is vital to ensure efficient operation of the heaters. Over time, resin deposits, dirt, and other contaminants can build up in the system and affect the heaters’ performance. Therefore, it is recommended to clean the hot runner system regularly using specialized cleaning solutions that do not damage the system’s components. It is also essential to avoid using sharp or abrasive tools during the cleaning process, as these can scratch or damage the heaters’ surfaces.

Hot Runner System Cleaning

Electrical Testing of Hot Runner Heaters, Thermocouples

Thirdly, to achieve optimal mold performance and part quality, it is essential to have precise control over the temperature of nozzles, bridges, and manifolds. This can be achieved by using the appropriate heater size (diameter and wattage) and thermocouple style, and ensuring they are installed correctly.

All heaters (sprue, bridge, manifold, nozzles) should be tested before usingm a typical ohmmeter may be used.

Heaters Insulation Resistance Testing

Heaters Insulation Resistance Testing

You can follow the steps:

  1. Ensure that the heaters (sprue, bridge, manifold, nozzles) being tested is completely de-energized and isolated from any potential power source.
  2. Connect the Megger to the heater.
  3. Set the Megger with a shot of high voltage (typically 500 VDC) to ensure the insulation material (most commonly magnesium oxide, MgO) is not compromised and allowing the electrical current from the element to bleed out to the sheath, which could lead to an early heater failure. Hitcontrols IR is min. 5 mega-ohms (cold) for unsealed, coil heaters or tubular heaters. In theory, a 1 mega-ohm IR reading is sufficient for 240V systems, as that would only be about 0.2mA of leakage current. (V = IR; I = 240V/1,000,000 ohms = 0.0002 amps)

It is important to follow safety procedures and use appropriate personal protective equipment during insulation resistance testing, as it involves working with potentially hazardous electrical equipment.

It is crucial to use high-quality components when repairing or replacing hot runner heaters. Low-quality or counterfeit components may seem like a cost-effective solution, but they can significantly affect the performance of the hot runner system and cause premature failure. Therefore, it is recommended to source replacement components from reputable suppliers and ensure they meet the manufacturer’s specifications.

For further information about hot runner heaters please contact HITCONTROLS team.

Thermocouple Testing

hot runner thermocouple testing

The first step is to install the thermocouple at the correct depth and prevent an air gap or excess plastic from insulating the tip from the nozzle. You should check the resistance of the thermocouple between 2 and 9 ohms using a 76 mm or less lead wire.

In addition, when replacing or cleaning thermocouples, it is important to avoid kinking them as it will either read at the kinked area or not at all. You should be extremely careful when bending and forming a new thermocouple to fit.

Finally, many multi-cavity molds have “left- and right-hand” positions, requiring thermocouples to be reinstalled in their original locations to avoid re-bending and risking breakage. Taking these precautions will ensure that your injection molding system performs optimally.

Keep the Heaters Clean and Dry

MgO is crucial as contamination is a more significant problem. Due to its hygroscopic nature, MgO readily attracts moisture, making it prone to damage. High-performance and high-watt-density hot-runner nozzle heaters are fully sealed to prevent contamination by moisture, oil, and other substances. However, the seal may get damaged during removal, cleaning or installation, leading to contamination. If moisture contamination is suspected in the MgO, “baking out” the heaters at a high temp can boil out the contaminants and regenerate the insulation value.

If you have heaters that have absorbed moisture, don’t worry! There are a few ways to resolve this issue.

  1. Using “soft-start”  function on a hot runner temperature controller. This method brings the heaters up to temperature gradually, from 0% to the setting. By doing so, any trapped moisture or contaminants can be slowly boiled out of the MgO insulation.
  2. Another solution is to place the unsealed heaters inside an oven to dry out the internal MgO insulation. An oven temperature in the 250 F range for an overnight cycle can sometimes work wonders and won’t damage or melt most lead-wire insulation.

Temperature Control

A temperature controller is vital for ensuring your hot runner system runs efficiently. Make sure to check your temperature controller regularly and calibrate it if necessary. This will help ensure your hot runner system runs at the correct temperature and prevent system failures.

Hot runner temperature controller trouble shooting guide.


Finally, it is essential to train personnel on proper hot runner heater maintenance and operation. This includes educating operators on the signs of wear or damage to look for, proper cleaning procedures, and how to test the heaters to ensure they are working correctly. A well-trained team can quickly identify potential issues and address them before they result in costly downtime.

In conclusion, hot runner heater maintenance is critical to ensuring optimal operation of hot runner systems and minimizing downtime in the injection molding process. A well-designed maintenance program that includes regular inspections, cleaning, and the use of high-quality replacement components can help prevent failures and extend the life of the system. Proper training of personnel on heater maintenance and operation is also essential to maintain a high level of production quality and efficiency.

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