Voron Heat Creep — Diagnosis and Prevention

Troubleshooting Hotend Printing

What Is Heat Creep?

Heat creep occurs when heat from the hotend travels upward through the heatbreak and into the heatsink, warming the filament before it reaches the melt zone. The filament softens prematurely in the heatbreak or heatsink area, becoming too pliable to be pushed forward by the extruder. This creates a jam that is not a clog — the filament is simply too soft to push. Heat creep is a progressive problem that gets worse over time as the heatsink temperature rises.

Symptoms of Heat Creep

• Random jams mid-print — The extruder stops extruding mid-print for no apparent reason. Resuming the print after cooling down and re-loading filament often works temporarily.
• Extruder clicking after long prints — The clicking (skipping) does not happen at the start of a print but develops after 30 minutes to several hours. This is the classic heat creep pattern.
• Filament grinding at the extruder — The drive gear grinds a flat spot into the filament. The softened filament deforms under the gear pressure instead of moving forward.
• Under-extrusion that gets worse over time — The print starts with normal flow, then gradually shows under-extrusion (gaps, thin walls) that worsens as the print progresses.
• Filament swelling at the heatbreak inlet — When removing filament after a jam, the tip is mushroomed or swollen, indicating it softened in the heatbreak area.

Causes of Heat Creep

Extruder Fan Not Running

The most common cause. If the hotend fan (heatsink fan) is not spinning, the heatsink quickly heat-soaks and transfers heat up the filament path. Check: fan plugged in, fan not obstructed by debris, fan wires not damaged, fan configured as always-on in Klipper.

Fan Duct Blocked or Inefficient

Debris (stringing, dust) can accumulate in the fan duct or on the heatsink fins, reducing airflow. The heatsink cannot dissipate heat, and creep begins. Clean the heatsink with compressed air and inspect the duct for obstructions.

High Chamber Temperature

Voron enclosures are sealed for ABS printing. When chamber temperature exceeds 50-60℃, the heatsink cannot shed heat because the ambient air is already warm. The heatsink temperature rises above the filament's glass transition temperature ( ~ 60-80℃ for PLA, ~ 100℃ for ABS), causing creep. This is why printing PLA in a Voron enclosure is difficult — PLA's glass transition temp is low.

Slow Print Speeds

At slow print speeds, filament spends more time in the heatbreak region, allowing heat to soak further up. Combined with a warm chamber, this accelerates heat creep.

High Retraction Counts

Frequent retractions pull molten filament up into the heatbreak where it cools against the walls and creates resistance. Each retraction deposits a small amount of molten plastic in the heatbreak, and over time this builds up into a jam.

Full Metal Hotend vs PTFE Lined

PTFE-lined heatbreaks (like the standard V6 or Creality style) have PTFE tubing inside the heatbreak that acts as a thermal insulator, reducing heat transfer to the filament. Full metal hotends (like the Dragon, Rapido, Mosquito) lack this insulator. The filament contacts the metal heatbreak walls directly, making them more susceptible to heat creep — but also capable of higher temperatures. The trade-off is that full metal hotends require better cooling.

Diagnosis Method: Temperature Tower + Fan Speed Test

To confirm heat creep is the issue:

1. Print a temperature tower at normal speeds. If jams occur at lower temperatures but clear up at higher ones, it is likely a clog, not creep. If jams occur at all temperatures, it is heat creep or a mechanical issue.
2. Print the same temperature tower with the enclosure door open and top panel removed. If the problem goes away, you have a chamber temperature / heat creep issue.
3. Run a dedicated heat creep test: print a tall cylinder (20mm diameter, 100mm height) at slow speed (40mm/s) with high retraction (1mm every 2mm of printing). If the extruder starts clicking above 60-80mm of Z height, heat creep is confirmed.

Fixes for Heat Creep

Hotend Fan Always-On Config in Klipper

The hotend fan must run whenever the hotend is hot. Do not use temperature-controlled fan triggers in Klipper that turn the fan off below a certain temperature. Use a heater_fan config with heater: extruder and fan_speed: 1.0. This keeps the fan running whenever the extruder heater is on.

Example Klipper config block:

[heater_fan hotend_fan]
pin: YOUR_FAN_PIN
heater: extruder
heater_temp: 0
fan_speed: 1.0

The heater_temp: 0 ensures the fan runs at any temperature above 0℃, i.e., whenever the hotend is active.

Fan Shroud / Duct Check

Inspect the fan duct for cracks or deformation (common in ABS printed parts over time). Ensure the duct directs airflow directly at the heatsink fins. StealthBurner toolheads have a specific duct design for the hotend fan — verify the fan is installed in the correct orientation (blowing toward the heatsink, not away from it).

Reducing Chamber Temperature

If you are printing ABS and the chamber is above 55-60℃, you need to manage enclosure temperature. Options:

• Open the top panel slightly (1-2cm gap) to let hot air escape.
• Open a side panel or door for the first part of the print, then close it once layer adhesion is established.
• Install a Nevermore or other chamber filter that actively circulates air (moving air = better heat dissipation).
• If printing PLA, keep the enclosure open or remove panels entirely.

Increasing Print Speed

Counter-intuitive, but faster print speeds mean the filament passes through the heatbreak faster, giving it less time to soak heat. If you are printing very slowly (under 50mm/s), increase speed to 60-80mm/s and see if the jams stop.

Heatbreak Upgrade

If you have persistent heat creep on a full metal hotend, consider upgrading the heatbreak:

• Bimetallic heatbreak (copper alloy + titanium or steel) — The copper portion conducts heat well into the melt zone, while the titanium or steel section above acts as a thermal barrier. This reduces heat transfer to the heatsink. Examples: Slice Engineering Copperhead, TriangleLab bimetallic.
• PTFE-lined heatbreak — If you do not need high-temperature printing (300+℃), a PTFE-lined heatbreak (like the standard E3D V6) provides better thermal isolation at the cost of reduced max temperature. For ABS and PLA (under 240℃), PTFE-lined may actually be more reliable against heat creep.

Heat Creep by Specific Hotend

Phateus Dragon

The Dragon has a bimetallic heatbreak from the factory. Heat creep is uncommon but can occur at very high chamber temps ( > 60℃). Ensure the heatsink fan is pushing air through the entire fin stack. The Dragon's heatsink is shorter than the Mosquito, so fan speed must be adequate.

E3D Revo

The Revo uses a heatbreak integrated into the nozzle (nozzle-heatbreak combo). Its tolerances are very tight. Heat creep occurs if retraction exceeds 0.5mm (pulls molten filament into the narrow heatbreak zone) or if the heatsink fan fails. Revo requires excellent cooling due to the short melt zone.

Rapido (Phateus)

The Rapido has a large heatsink designed for high-flow printing. It is less prone to heat creep than the Dragon. However, at 40W+ heater power, the Rapido generates significant heat. The heatsink fan must be high-quality (a 40x20mm fan at 100% is recommended).

Slice Mosquito

The Mosquito has the largest heatsink of common Voron hotends. Heat creep is rare. If it occurs, check the fan orientation — the Mosquito fan must blow into the heatsink. The Magma hotend (high-flow version) adds even more thermal mass but also more heat, so fan requirements are higher.