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Hot Runner Temperature Controller Troubleshooting: Common Problems and Solutions

Hot runner systems are essential for precise temperature control in plastic injection molding. A well-functioning hot runner temperature controller ensures consistent product quality, reduces material waste, and improves cycle efficiency. However, like any electronic system, it can encounter problems over time.

In this guide, we’ll cover the most common hot runner temperature controller issues—including uncontrolled temperature changes, PV display alarms (HI, HHH, LLL)—and provide practical troubleshooting solutions.

Why Is Hot Runner Temperature Control Important?

Hot runner systems maintain molten plastic at the correct temperature inside the manifold and nozzles. If temperature control fails, it can lead to:

Part defects (short shots, flashing, burn marks)

Increased downtime

Higher maintenance costs

Potential safety hazards

By learning how to quickly diagnose and fix issues, you can minimize downtime and keep your production line running smoothly.

What Does The Accuracy And Stability Of Temperature Control Mainly Depend On?

Temperature Measurement: Sampling period parameters, data filtering, and temperature compensation in the measurement circuit determine temperature measurement accuracy.

PID Control: This controls the output current proportionally. Related parameters include the proportional range, integral time, and derivative time.

PIDD Control: This controls the phase angle. Related parameters include the proportional range, integral time, and derivative time.

Automatic Adjustment: This function analyzes the capacitance of the heating wire and the thermal constant of the mold to provide the dominant factor. It has latent heat and heat dissipation properties, enabling precise temperature control regardless of environmental fluctuations.

Output Mode: SSR (PIDD) Mode. This mode achieves precise temperature control; however, the power supply noise is significantly greater than in PWM Mode.

PWM (PID) Mode: This mode offers low current noise, but its ability to control a specific temperature is inferior to SSR Mode.

Common Hot Runner Temperature Controller Problems and Fixes

Uncontrolled Temperature Drop (PV Screen Indicates a Sudden Drop)

Symptoms:

The temperature on the PV (Process Value) screen drops suddenly and uncontrollably.

System fails to maintain set temperature.

Possible Causes:

Broken heating element wiring.

Burned-out heating element.

How to Fix:

Immediately turn off the hot runner temperature controller power to prevent accidents.

Inspect wiring for any disconnections or damage.

Replace the faulty heating element if necessary.

PV Screen Displays “HI” with Alarm Beeping

What Does “HI” Alarm Mean?
The PV display shows HI when the system detects that the actual temperature has exceeded the upper deviation limit of the set temperature or when there is interference from other heat sources.

Solutions:

Switch to manual mode, then reduce the power output percentage (AN) to lower the temperature.

Stop the injection process and allow the system to cool down.

Identify and eliminate any external heat sources that might be causing interference.

PV Screen Shows “HHH” with Alarm

Causes:

Thermocouple circuit is open, leading to a high positive voltage input signal.

Temperature controller output is not connected to the heater load.

Solutions:

Check the thermocouple wiring for any disconnection or damage.

Replace the thermocouple if necessary.

Ensure the heater circuit is properly connected to the controller output.

PV Screen Displays “LLL” with Alarm

Causes:

Thermocouple polarity is reversed, causing an excessive negative input signal.

Solutions:

Correctly connect the thermocouple positive and negative leads.

Safety Tips for Hot Runner Controller Maintenance

Always disconnect the power before performing any inspections or repairs.

Use proper thermal gloves and PPE when handling hot runner components.

Keep the controller free from dust and moisture to avoid short circuits.

When to Call a Professional?

If you have tried the above troubleshooting steps and the problem persists, it might be time to contact your hot runner system supplier or an experienced technician. Continuous alarms or inconsistent heating can indicate deeper electrical or component issues that require expert attention.

Conclusion

Proper maintenance and timely troubleshooting of your hot runner temperature controller can prevent costly downtime and improve the efficiency of your injection molding operations. Bookmark this guide as your quick reference for solving common issues like uncontrolled temperature, HI alarms, HHH/LLL errors.

Need expert support or replacement parts? Contact us today for high-quality hot runner controllers and professional technical assistance.