What Can Cause Hotend Temperature Fluctuations? (How to Fix?)

One of the most vital things to keep in mind while operating a 3D printer is that the hotend can reach extreme temperatures, which makes following safety precautions, such as not leaving the printer unattended as it’s functioning, integral for safety.

While most modern 3D printers have protection in place for scenarios where the hotend malfunctions and reaches dangerous temperatures, we believe that the best course of action is to take our own safety precautions and take the process of 3D printing seriously due to the dangers that are involved.

Today, our topic is a rare but critical issue that will be highly problematic for the printing process and also has the capability of causing environmental dangers, known as hotend temperature fluctuations, where the temperature of the hotend doesn’t stabilize after the hotend heats up.

So, what can cause hotend temperature fluctuations?

Below, we have listed the common reasons that can cause your 3D printer to have hotend temperature fluctuations:

  • Incorrect PID tuning
  • Misconfigured thermal runaway protection parameters
  • Problems with the thermistor
  • Issues with the heating block

Moving forward, we will examine the possible reasons behind the hotend having temperature fluctuations, find out what we can do to stabilize the hotend temperature, and discuss the signs to look out for in scenarios where it looks like the hotend temperature isn’t staying stable.

What Can Cause Hotend Temperature Fluctuations?

As there are a fair few different parts that work together to make the hotend operational, a problem with any of these parts could be the reason behind the hotend temperature fluctuations you’re facing, making it challenging to find the root cause.

Here are the common potential culprits behind hotend temperature fluctuations, alongside detailed explanations that clarify how these culprits can cause the problem:

  • PID tuning incorrect – PID tuning refers to the configuration of the P (proportional), I (integral), and D (derivative) values that the printer uses to handle temperature adjustments, and these values need to be correct for the 3D printer to be able to hold the hotend temperature steady.
  • Firmware thermal runaway protection misconfiguration – The thermal runaway protection feature consists of two parameters (hysteresis and period) that determine when the protection kicks in. Misconfiguring these values can cause hotend temperature fluctuations by causing the 3D printer to power the heat cartridge off, which is the natural response when a thermal runaway is imminent.
  • Thermistor issues – The thermistor is responsible for reading the temperature of the heat block and reporting it, which is what the 3D printer uses to display the temperature data to the user. An issue with the positioning of the thermistor, faulty wiring, or a faulty thermistor itself can throw these readings off, causing hotend temperature fluctuations.
  • Heating block problems – The heating block is responsible for heating the hotend and supplying the necessary temperature levels for the 3D printing process. Issues related to the seating or the wiring of the heat block or the heat block unit itself can cause hotend temperature fluctuations.

Please keep in mind that this list is not exhaustive, as any component that impacts the regulation of the hotend temperature can technically contribute to the hotend temperature fluctuations problem.

How to Fix the Issue of Hotend Temperature Fluctuations?

As the hotend temperature fluctuations can occur due to various problems with the 3D printer, the best course of action is to check every component that can be a possible culprit and apply the appropriate fix in the case of a malfunction.

Below, we have created a checklist that includes the fixes for the most common culprits behind the problem of hotend temperature fluctuations, which we recommend following on a step-by-step basis.

  • Auto-tune the PID values – Running the PID auto-tune (M303 in Marlin) command for the print temperature value you will be using whenever you modify it is highly recommended to ensure that the 3D printer can regulate the hotend temperature correctly.
  • Re-configure the thermal runaway protection – As it’s best to keep the default thermal runaway protection parameters, we only recommend a re-configuration if you have manually changed these values before since incorrectly configuring these parameters can create worse results, such as the thermal runaway protection not triggering at all.
  • Maintain (or replace) the hotend thermistor – We recommend ensuring that the hotend thermistor is in the correct position and doesn’t have problems related to wiring. If the problems persist, a replacement can be necessary.
  • Maintain (or replace) the hotend heat block – We recommend ensuring that the heat block is seated correctly, that the wires are connected correctly and aren’t damaged, and finally, completely replacing the heat block.

How to Identify Hotend Temperature Fluctuations?

Temperature fluctuation on the hotend is a critical problem, which makes identifying it as quickly as possible and taking the necessary precautions vital in the case of suspicion that the hotend isn’t behaving as intended.

You can track the hotend temperature through the screen of your 3D printer or by using 3D printing interfaces that allow you to see detailed information about the current printing process (such as OctoPrint) and find out if the hotend temperature is fluctuating.

On the other hand, if you suspect that there is an issue with the hotend thermistor, you can also obtain external temperature readings of the hotend with a thermocouple and compare them to the values from the thermistor.

Aside from observing the values, observing the print itself for indications such as under-extrusion or over-extrusion in some regions, which can take place due to the plastic reaching temperatures that aren’t optimal, can also be helpful to identify hotend temperature fluctuations.

What Are the Dangers of Hotend Temperature Fluctuations?

Depending on what’s causing it, hotend temperature fluctuations can be quite dangerous, as these fluctuations essentially mean that the 3D printer is either unable to stabilize the hotend temperature or unable to take a stable reading of the temperature.

The primary danger of hotend temperature fluctuations is the possibility of the hotend reaching a temperature above the levels that are safe for the 3D printer, which can damage the equipment or even start a fire in more severe cases.

Such a scenario can quickly occur if the 3D printer thinks that the temperature of the heating block is less than its actual value due to a factor such as a thermistor reporting the wrong values and keeps increasing the temperature, creating the issue known as a thermal runaway.

As the consequences can be very severe in such situations, we highly recommend activating the firmware’s thermal runaway protection feature, preventing such occurrences.

Wrapping Up

As the problem of hotend temperature fluctuations is one that you should never ignore, no matter what’s causing it, we highly recommend immediately halting all operations with the 3D printer until you resolve the issue.

To quickly recap, issues on the software front, such as tuning the PID values incorrectly or misconfiguring the thermal runaway protection of the 3D printer firmware, and issues with hardware, such as issues with the thermistor and the heating block, can all contribute to the problem of hotend temperature fluctuations.

As the hotend of a 3D printer already operates at very high temperatures, fluctuations that cause the temperatures to spike even higher can create quite dangerous conditions, making it vital to solve this problem before conducting another printing process.

Happy printing!