Why Won’t My Print Cooling Fan Start?

Your print cooling fan won’t start because you’re missing M106 commands in your G-code or have incorrect slicer settings. Check if your slicer’s default fan speed is set to zero, which disables cooling entirely. Verify that M106 S255 commands appear in your G-code file to activate the fan at full speed. Hardware issues like loose connections, damaged wiring, or blown transistors can also prevent fan operation. The troubleshooting steps below will help you identify and fix the specific cause.

Common G-Code Commands Missing for Fan Control

When your print cooling fan refuses to start, the culprit is often missing or incorrect G-code commands that control fan operation.

The M106 command is essential for activating your cooling fans during printing. You’ll need M106 S255 in your fan gcode to turn the fan on at full speed, while M107 turns it off completely.

Essential cooling fan control requires M106 S255 to activate at full speed and M107 to completely shut off operation.

Check your G-code file for these critical commands. If they’re missing, your cooling fans won’t activate automatically during the print process. This absence typically stems from slicer configuration issues where auto cooling commands aren’t properly generated.

You should verify that your slicer includes fan control commands in the final G-code output. Without proper M106 commands embedded in your file, you’ll face cooling problems that can cause print deformation and quality issues.

Slicer Software Settings Configuration Issues

Your slicer’s configuration directly controls when and how your cooling fan operates during printing.

You’ll need to check three critical areas: your default fan speed settings, whether the slicer’s generating the proper G-code commands, and how you’ve configured layer-based cooling parameters.

If any of these settings aren’t properly configured, your fan won’t start when it should.

Default Fan Speed Settings

The complexity of modern slicer software often masks simple configuration oversights that prevent print cooling fans from activating. Your default fan speed settings might be set to zero, effectively disabling cooling throughout your entire print.

Check your slicer’s cooling section where initial fan speeds are configured. You’ll often find settings labeled “Initial Fan Speed” or “Minimum Fan Speed” that need adjustment. Even if auto cooling is enabled, these baseline settings control when your fan starts working.

Your gcode should contain M106 commands with appropriate speed values – M106 S255 represents full speed while lower S values indicate reduced speeds.

Don’t overlook the “Fan Speed at Layer Height” setting, which determines when cooling begins relative to your print’s progress.

Missing G-code Commands

Beyond simple speed configurations, your slicer mightn’t be generating the necessary fan control commands at all.

When your fan works during manual testing but fails during prints, missing M106 commands in your gcode file are likely the culprit.

Your slicer must include specific G-code commands to control fan operation:

1. M106 S commands to set fan speed (S0-S255 range)
2. M107 commands to turn fans off when needed
3. Proper timing for when these commands execute during print layers

Software updates can reset custom machine profiles, removing fan configurations you’ve previously set.

Always review your generated G-code before printing, specifically searching for M106 S commands. If they’re absent, revisit your slicer’s cooling settings and confirm fan control options are properly enabled in your machine profile.

Layer-Based Cooling Configuration

While basic fan control commands might exist in your G-code, improper layer-based cooling configuration can prevent your print cooling fan from activating when needed. Your slicer’s cooling settings determine when fans start operating during the printing process.

Most slicers disable cooling for the first layer to guarantee proper bed adhesion. However, incorrect configuration might extend this delay beyond necessary layers. Check your cooling tab settings to verify fan activation timing.

Setting	Recommended Value	Purpose
First Layer Fan Speed	0%	Prevents warping
Regular Layer Fan Speed	50-100%	ideal cooling
Fan Activation Layer	Layer 2-3	Material dependent

Your slicer generates specific G-code commands like M106 based on these configurations. If layer-based cooling configuration isn’t properly set, fans won’t activate correctly throughout your print.

Hardware Connection and Wiring Problems

When your print cooling fan refuses to start, faulty hardware connections often serve as the primary culprit behind this frustrating issue.

Part Cooling Fan never operates properly when wiring problems exist, so you’ll need to systematically check your connections before you start a print. Creating a new account of your fan’s behavior helps identify patterns.

Follow these essential troubleshooting steps:

1. Inspect the fan plug connection – Verify it’s fully seated in the mainboard socket and check for loose contacts.
2. Examine wiring for damage – Look for frayed, bent, or broken wires that could interrupt power flow.
3. Clear debris around the fan – Remove any obstructions that might prevent mechanical operation.

Try reversing the plug orientation if standard connection fails, as misalignment sometimes causes connectivity issues.

Firmware Compatibility and Update Requirements

After ruling out hardware connection problems, firmware compatibility issues represent the next logical troubleshooting step for non-functioning print cooling fans.

Your printer’s firmware controls how hardware components communicate, particularly regarding fan commands like M106 and M107. When you update firmware, some versions might revert to older fan configurations that don’t match your slicer’s G-code output.

You’ll need to verify your firmware version matches your specific printer model to prevent unexpected fan behavior.

Check manufacturer release notes after updates, as they’ll detail changes affecting fan operation. Some firmware updates resolve fan activation bugs, while others might introduce compatibility issues with slicing software like Cura or PrusaSlicer.

Regular updates typically improve functionality, but always confirm compatibility first.

Manual Fan Testing Through Printer Interface

You can manually test your cooling fan by accessing your printer’s control menu or interface panel.

Navigate to the fan controls section and use commands like M106 S255 to run the fan at full speed, which helps verify if it’s functioning properly.

If the fan operates during manual testing but won’t start during actual printing, you’ve likely identified a G-code or slicer configuration issue rather than hardware failure.

Accessing Printer Menu

How can you determine if your print cooling fan itself is functioning properly? Start by accessing your printer’s main menu through its control interface. You’ll need to navigate to the calibration or settings section where fan controls are typically housed.

Here’s how to proceed with manual testing:

1. Locate fan controls – Find the fan control menu within your printer’s settings or calibration section.
2. Activate the fan – Select the option to turn it on, often using commands like M106 S255 for full speed operation.
3. Observe operation – Watch and listen to confirm the fan runs smoothly without unusual noises or obstructions.

If your fan doesn’t respond during this manual test, check all wiring connections to verify they’re properly seated and free of damage or dust accumulation.

Testing Fan Commands

Manual fan testing through your printer’s interface provides the most direct method for isolating whether your cooling fan hardware functions correctly.

Navigate to your printer’s calibration or settings menu where you’ll find fan control options. You can activate the fan manually using G-code commands like M106 S255 for full speed or M107 to turn it off.

During testing, observe the fan’s immediate response. It should start without delay—any hesitation suggests wiring or connectivity problems.

If your fan operates correctly when manually activated, the hardware’s functional, indicating software settings or G-code commands are likely causing issues.

When fans pass manual tests but fail during printing, review your G-code file and slicer settings for fan operation commands.

Verifying Speed Controls

Once your printer responds to basic on/off commands, you’ll need to verify that speed controls function across the full range of operation.

Navigate to your printer’s LCD interface and access the fan control settings to test different speed levels manually.

Follow these verification steps:

1. Test minimum speed – Set the fan to its lowest operational setting to confirm it starts reliably at reduced power levels.
2. Check maximum speed – Increase to full speed (100%) and listen for consistent operation without unusual noises or vibrations.
3. Verify intermediate levels – Test 25%, 50%, and 75% speeds to guarantee smooth changes between settings.

If manual controls work but your fan doesn’t respond during prints, the issue likely stems from incorrect M106 G-code commands in your slicer’s cooling settings rather than hardware malfunction.

Layer Height and Cooling Timing Settings

While troubleshooting cooling fan issues, you’ll need to examine how your layer height and cooling timing settings interact to determine if they’re preventing your fan from activating properly.

Thinner layers require more aggressive cooling to prevent deformation, so check if your current settings match your layer height requirements. Most slicers keep fans off during the first layer by default to improve bed adhesion, but you can modify this for materials like PLA that benefit from earlier cooling activation.

Review your fan timing settings in Cura or PrusaSlicer to guarantee the fan starts when needed. Consider gradually increasing fan speed over multiple layers rather than immediate full activation to prevent warping while maintaining proper cooling throughout your print.

Mainboard and Transistor Failure Diagnosis

When your cooling fan won’t respond to G-code commands like M106, you’re likely dealing with a blown transistor on your mainboard that’s preventing power delivery to the fan.

You’ll need to inspect your board for visual damage like burnt components or unusual smells, then consider whether a complete board replacement is necessary.

If replacement isn’t immediately feasible, you can explore firmware workarounds that redirect fan control to alternative ports on your mainboard.

Blown Transistor Symptoms

A blown transistor on your mainboard can silently sabotage your print cooling fan’s operation, creating a frustrating scenario where the fan works perfectly when you test it manually but refuses to start during actual prints.

You’ll notice several telltale signs when dealing with transistor failure:

1. Intermittent fan behavior – Your fan sporadically responds to commands, working sometimes but failing unpredictably during critical print moments.
2. Unresponsive G-code commands – The fan won’t activate when you send M106 S255 commands through your printer interface.
3. Unusual heat generation – The transistor area feels noticeably warmer than normal during operation.

Visual inspection often reveals burn marks or physical deformation around the transistor itself.

Testing voltage output at transistor pins when the fan should operate confirms failure if you’re getting zero voltage readings.

Board Replacement Process

Once you’ve confirmed transistor failure through voltage testing and visual inspection, replacing your printer’s mainboard becomes the most reliable solution to restore fan functionality.

Start by powering down your printer and carefully disassembling the control box to access the mainboard. Document wire connections with photos before disconnecting them to guarantee proper reassembly. Remove the old board and install the replacement, securing all connections firmly to prevent future issues.

After installation, you’ll likely need to reflash the printer’s firmware to guarantee compatibility with fan control settings and G-code commands.

If immediate replacement isn’t possible, you can temporarily reassign fan ports in firmware to use a different output, allowing continued operation until you obtain the new mainboard.

Firmware Port Workarounds

If your mainboard’s fan port has failed but you can’t immediately replace the board, firmware port reassignment offers a temporary solution to keep printing.

You’ll need to access your printer’s firmware configuration and redirect fan control to an alternative port that’s still functional.

Here’s how to implement this workaround:

1. Identify available ports – Check your mainboard documentation for unused fan headers or auxiliary outputs that can handle your cooling fan’s power requirements.
2. Modify firmware settings – Access your printer’s configuration files and reassign the part cooling fan from the failed port to your chosen alternative port.
3. Test functionality – After reflashing the firmware with updated settings, verify the fan responds correctly to cooling commands during a test print.

This approach keeps you printing while sourcing replacement components.

Plugin Conflicts in OctoPrint and Print Servers

When you’re running OctoPrint or other print servers, plugin conflicts can silently sabotage your print cooling fan’s performance by intercepting and overriding the standard G-code commands that control fan operation.

These conflicts typically affect M106 and M107 commands, causing fans to activate at wrong times or run at incorrect speeds.

Plugin conflicts disrupt M106 and M107 commands, triggering fan malfunctions with improper timing and incorrect speed control during prints.

To troubleshoot this issue, you’ll need to disable all non-essential plugins temporarily. This isolation method helps you identify which specific plugin is causing the problem.

Check for plugin updates regularly, as newer versions often resolve existing conflicts that impact fan functionality.

The OctoPrint community actively shares experiences with problematic plugins, so you can search forums for known issues with your installed plugins before spending time troubleshooting independently.

Fan Speed Ramping and First Layer Adhesion Settings

While many users assume their print cooling fan isn’t working when it doesn’t activate immediately, most slicers deliberately keep the fan off during the first layer to improve bed adhesion.

Cura’s default cooling settings exemplify this approach, but you can customize the behavior through fan speed ramping configurations.

To optimize your cooling strategy, consider these key settings:

1. Initial Fan Speed: Set your first layer fan speed to zero, then gradually increase for subsequent layers.
2. Layer-Based Ramping: Configure specific fan speeds for different layer heights to prevent warping while guaranteeing adequate cooling.
3. Minimum Layer Time: Adjust this setting to guarantee sufficient cooling time, as shorter layer times can cause print deformation.

For materials like PLA, activating the fan after the first layer prevents sagging and maintains print quality throughout the process.

Physical Obstruction and Mechanical Binding Checks

Start by examining the fan blades for debris, dust, or filament fragments that could block rotation. Manually turn the blades to test for smooth movement—any resistance indicates binding issues.

Check Type	Action Required	Common Issues
Visual Inspection	Remove debris/obstructions	Dust, filament bits
Manual Rotation	Turn blades by hand	Mechanical binding
Housing Alignment	Verify mounting position	Misaligned components

Next, check the fan’s mounting and housing for misalignments causing physical interference. Confirm the connector’s securely seated without wire damage. Regular cleaning prevents dust buildup that leads to performance issues and overheating.

Frequently Asked Questions

Why Is My Cooling Fan Not Kicking In?

Your cooling fan might not start because you’re missing M106 commands in your G-code, have incorrect Cura settings, loose wiring connections, or outdated firmware that’s preventing proper fan activation.

What to Do if My Cooling Fan Is Not Working?

Check your G-code for M106 commands, verify slicer settings like “Keep fan always on,” inspect wiring connections, test the fan manually using M106 S255, and update firmware if needed.

How Do I Know if My Cooling Fan Relay Is Bad?

You’ll know your cooling fan relay’s bad if you don’t hear clicking when activated, see burn marks or corrosion, or measure no continuity across terminals with a multimeter during engagement.

Should the Radiator Fan Come on When the Car Starts?

Your radiator fan shouldn’t start immediately when you start your car. It’ll only activate once your engine reaches operating temperature, typically around 200°F, or when you’re using air conditioning.