BLTouch Blinking Red – What Causes It and How to Fix It?

A BLTouch is quite a simple device, and as a result, it doesn’t feature a screen or any other complex interface that can directly inform you of any problems. That being said, it does come with a couple of LED lights instead, which we can use to diagnose the status of the probe.

In this guide, we will explain the meanings behind the two distinct states of BLTouch red LED blinking (fast blinks and slow blinks), the causes behind their occurrence, and how you can fix the indicated problems to get your BLTouch in working order once again.

Causes & Fixes for BLTouch Blinking Red – Fast Blinks (50% Duty)

A BLTouch with its red LED light blinking fast gives us the information that it’s currently in alarm mode as a result of either failing the self-test process that it undergoes before leveling or failing to operate as intended during the leveling process itself, which a few different factors can cause.

bltouch alarm mode cycle

BLTouch Pin Physically Unable to Move

The pin of the BLTouch being physically restricted is the most common reason that can cause a BLTouch to blink red, as wear and tear over time can make it difficult for the pin to move.

Factors such as dust and dirt making their way into the housing, the magnetic screw that pulls the pin getting looser, the pin getting bent, and problems with the magnetization of the screw or the pin can all contribute to this problem, prompting the BLTouch to go into alarm mode.

While there are a few more reasons that can prevent the movement of the pin, a physical restriction is the very first one we recommend checking for due to it being the easiest one to confirm and fix.

Pin Doesn’t Stow

If you’re experiencing a scenario where the pin always stays in the deployed position and is unable to be stowed, start by trying to push the pin up gently, preferably not directly with your finger (to avoid getting dirt on the pin), and see whether it can move up freely.

In the case where the pin doesn’t smoothly go inside the case once you push it up, the first step you will need to take is to remove the pin from the case, inspect it for bending, and straighten it (or replace it) if it’s indeed bent.

While you have the pin out of the case, it’s a good idea to give the pin and the inside of the BLTouch case a thorough cleaning by spraying them with some electronic cleaner, which will rule out the possibility of dirt causing the problem.

Once that’s done, place the pin back inside the case, and test your BLTouch to see if anything has changed.

If the problem continues with the pin moving freely, further tighten the magnetic screw on the top of the BLTouch probe to push it closer to the pin, and try testing your BLTouch again. In most cases, the BLTouch failing to stow the pin results from the magnetic screw being too far away, which makes it unable to pull the pin upward.

Remember to re-adjust your Z-offset value after tightening the magnetic screw.

If tightening the magnetic screw does not solve the problem, follow up with re-magnetizing both the pin and the screw by leaving them attached to a strong magnet for 10-15 minutes, which will ensure the magnetic qualities of the parts are intact.

Additionally, if you didn’t need to take the pin out in the earlier step, now is an excellent time to perform the cleaning.

Once you get the re-magnetizing done, you can re-assemble (refrain from touching the pin with your bare hands to avoid getting dirt on it) and test your BLTouch again.

Pin Doesn’t Deploy

If the pin of your BLTouch is stuck in the stowed position, start by completely unscrewing the magnetic screw on the top of the BLTouch, which should release the pin.

Next, push the pin up a few times with the help of a clean object, and see whether it’s able to move up and down freely without the magnetic screw in place.

If the pin cannot move freely, take it out of the case, inspect it for bending, and straighten (or replace) it if any bending is present.

Additionally, clean the inside of the BLTouch case and the pin itself by spraying electronic cleaner, as dust and dirt can obstruct the pin movement as well.

Provided that the pin comes down smoothly (you can test it a few more times by pushing the pin up and observing whether it’s able to move up and down without obstruction), put the magnetic screw back into its position, but leave it looser than it was before, and test your BLTouch.

Leaving the magnetic screw at a looser state will increase its distance to the pin, making it less likely that the pin gets pulled up inadvertently.

Misconfigured (Incompatible) Firmware

Another common factor that can cause your BLTouch to blink red is the usage of misconfigured firmware, as the firmware needs to be made aware of facts such as the existence of a BLTouch, and how it’s connected to the mainboard.

Issues such as the BLTouch parameter not being enabled at all or the servo pin and the Z probe pin being configured incorrectly in the firmware config can contribute to the occurrence of this problem and cause your BLTouch to blink red.

marlin firmware z probe options

With misconfigured firmware, you can observe signs such as the pin deploying and stowing without issues but the leveling failing with the nozzle potentially crashing into the print bed (incorrect Z probe pin) or the pin not stowing and deploying (incorrect servo pin), depending on how the firmware is configured.

If you suspect that the firmware is the culprit, the most straightforward way to rule out any firmware-related problems would be to find and flash the official BLTouch-enabled firmware for your 3D printer, which will guarantee the firmware is correctly configured for BLTouch usage.

Incorrect or Problematic Wiring

Ruling out issues related to wiring is practically impossible when talking about any malfunctioning 3D printer component, and the BLTouch is no exception.

Factors such as the wires being connected to the incorrect pins (black wire going where white wire is supposed to go, and vice versa), physical damage to one or more of the wires or connectors, and loose connections are the first things that come to mind in this case, which are all highly likely.

Similar to misconfigured firmware, common signs you can come across with wiring-related issues would be the leveling not working correctly and potentially causing the printhead to crash into the bed (problem with trigger wires) or the pin not moving at all (problem with servo wire), depending on which wires are problematic or misconnected.

To rule out wiring-related problems, we first recommend pulling the BLTouch cable out from both ends and inspecting that there is no damage to any of the wires. Kinked wires, the wire sheats being damaged, and connectors coming loose off the wires are some of the common signs to look for.

Next up, we would recommend directly referring to the BLTouch wiring page, where you can find diagrams that explain how to connect a BLTouch to various types of mainboards correctly and to connect the wires accordingly.

Finally, the last step is to ensure that the connectors are sitting tightly in their places, with no signs of wobbling that would indicate the connection is loose.

If the problem continues after ensuring that the wiring is correct, replacing the BLTouch cable is also worth giving a try before looking for the issue elsewhere.

Probe & Z Homing Feed Rate Too Slow

While a rare case, using a probe or Z homing feed rate value that is way too low is also known to cause BLTouch probes to go into alarm mode and start blinking red.

Since the probe and the Z homing feed rate values control how quickly the printhead moves during probing and homing, values that are too low will cause the printhead to move way too slowly and potentially lead to the BLTouch timing out before it makes contact with the print bed.

In such a case, there shouldn’t be any issues with the BLTouch itself, and the pin stowing and retracting as intended (you can use manual commands to verify) is the most visible sign that would confirm this.

With this in mind, if the blinking happens while the printhead moves to the following probing location (X and Y axes), you will need to increase the XY_PROBE_FEEDRATE (Configuration.h) value, which determines the XY speed during probing.

On the other hand, if the red blinking occurs while the printhead is moving in the Z-axis (approaching the bed) during probing, Z_PROBE_FEEDRATE_FAST (Configuration.h) is the parameter that will require a higher value, which is responsible for the Z-axis movement speed during the first approach.

marlin firmware probe feedrates

Alternatively, in the case where the red blinking happens during homing, specifically when the printhead is getting closer to the bed for the probe to take a reading, you will need to take a look at the HOMING_FEEDRATE_MM_M (Configuration.h) parameter and increase the third value in specific, which controls the homing speed for the Z-axis.

marlin firmware homing feedrate

Finally, when you adjust any of the parameters mentioned above, make sure to increase the DEFAULT_MAX_FEEDRATE (Configuration.h) values accordingly as well, as none of the feed rate values can exceed the specified max feed rate for each axis.

marlin firmware max feedrate

Once you make the necessary adjustments to the parameters in the Configuration.h file, you will need to build the firmware from the source code and flash it to your 3D printer for the changes to take effect.

Defective BLTouch

Finally, if nothing else seems to be creating the problem, the BLTouch itself being defective can be the reason, which is specifically common with inauthentic BLTouch clones sold as original BLTouch probes in many places.

For such a scenario, our first recommendation is to verify whether your BLTouch is genuine by entering the serial number printed on the PCB (next to the QR code) into the BLTouch Validation website.

If your BLTouch is indeed genuine, you will be greeted with the message that tells you so, along with the manufacturing date of the probe.

bltouch genuine

In this case, we recommend contacting ANTCLABS directly about your problem, along with the details of what you have tried so far, and they should be able to help you.

On the other hand, if there is no serial number printed on the PCB or the website tells you that your BLTouch is not genuine, then the best course of action would be to purchase an authentic BLTouch and discard the one you currently have.

bltouch not genuine

While authentic BLTouch probes certainly aren’t exempt from problems, the chance of having issues with a clone is far greater.

Causes & Fixes for BLTouch Blinking Red – Slow Blinks (80% Duty)

The red LED of a BLTouch blinks slowly when the BLTouch receives control signals from the 3D printer despite not being powered on, which can mean two different things based on the point at which the blinking starts.

bltouch slow blink cycle

Slow Blink Right After 3D Printer Powers On

If the slow blinking starts right after you power your 3D printer on, it’s a warning sign that there could possibly be a problem regarding the red (+5V) wire, but not necessarily, as the control signal from the printer can arrive before power does and trigger this response even when the BLTouch is powered correctly.

In this case, the recommended course of action is to run the Alarm Release command by sending either the M280 P0 S60 (Alarm Release & Touch Switch Mode) or the M280 P0 S60 (Alarm Release & Stow Pin) G-code to your 3D printer.

Provided that there are no issues with the red wire and that your BLTouch is receiving power as expected, the Alarm Release command should stop the blinking of the red LED, informing you that your BLTouch is ready to use.

On the other hand, if the slow blinking continues after the Alarm Release, it’s a sign that there is actually a problem regarding the red (+5V) wire and that your BLTouch is not receiving power as it should.

In this case, we recommend reading the following section, where we will discuss solutions for the scenario where it’s confirmed that the red wire is compromised.

Slow Blink During Operation

If the slow blinking starts while the BLTouch is operating, during 3D printing, or practically any other time when your 3D printer has been powered on for some time now, it means that the BLTouch has lost power from the red (+5V) wire.

In this case, we recommend removing the cable that connects the BLTouch to the mainboard from both ends and carefully inspecting the red wire and the connectors for any signs of physical damage, such as the wire being bent, the sheath of the wire being compromised, or the connector being loose from either end.

If there is no physical damage you can see on the wires, the next step is to reconnect the wires while ensuring that both connectors sit tightly in their places, and try again, as a loose connection can sometimes cause this problem even if the wire isn’t damaged.

In the scenario that the problem still continues, our next and final recommendation (before replacing the BLTouch itself) would be to replace the cable, as it’s definitely possible for the cable to be compromised even if it’s not visible from the outside.


Now that you know the meaning of the different red LED blink patterns that your BLTouch can produce, the causes behind them, and the corresponding solutions, you can quickly decipher what’s creating the issue in your case and hopefully fix your BLTouch.

While solutions such as re-flashing the firmware, disassembling the BLTouch, and going through wires aren’t very user-friendly, specifically if you aren’t too technically inclined, it is usually possible to solve the problem without replacing the probe.