Why Is My BLTouch Blinking Red & How Can I Fix It?

Installing an auto bed leveling probe to your 3D printer is perhaps the most significant improvement you can add to the 3D printing process, especially considering the importance of proper bed leveling for successfully printed models.

When auto bed leveling is the topic, BLTouch is the name that comes to mind as the most popular probe on the market right now, also creating the most popular printer and probe combination together with the Ender 3 that it supports.

As with everything else in the 3D printing realm, the BLTouch can come with problems of its own at times, with the issue of a red blinking light being the most commonly talked about one in the community, which will be our topic today.

So, what can cause the BLTouch to blink red?

BLTouch blinking red quickly (equal times on and off) means that the probe is in alarm mode, signaling that it has failed the self-test, which can be due to various things going wrong, such as the obstruction of the pin.

On the other hand, BLTouch blinking red slowly (more on than off) is a sign that there is an issue with the 5V or GND wire, such as incorrect wiring or wire damage.

In the upcoming sections, we will analyze the BLTouch blinking red issue in more detail, discuss the methods you can use to fix this issue, and take a look at a few other BLTouch LED flashing patterns that signify other problems.

Why Is My BLTouch Blinking Red?

A flashing red light is almost always a sign that something is wrong, and unfortunately, it’s no different in the case of the BLTouch either.

The BLTouch can blink red in two different patterns, where the blinking is fast in one (50% uptime of the LED) and slow in the other (80% uptime of the LED), with each pattern signaling a separate issue.

BLTouch Blinking Red Quickly

The first BLTouch red LED pattern that signifies an error is when the LED flashes quickly with an uptime of 50%.

A quickly flashing red LED on the BLTouch tells us that the BLTouch is in alarm mode due to failing the self-test process where the probe conducts the necessary checks before becoming ready.

As the BLTouch going into alarm mode can be a result of many different things that go wrong during the self-test process, here is a list of the common culprits that accommodate most cases but isn’t exhaustive:

  • Obstruction of the pin, causing it to be incapable of moving up and down freely, which can be due to either internal factors (damaged probe) or external factors (dust, dirt, etc.)
  • The pin hitting the build plate
  • Issues with the homing of the Z-axis, such as the speed being too slow
  • Physical damage to the probe, preventing the pin from functioning correctly
  • Firmware issues
  • Defective probe

While this list isn’t exhaustive by any means, as we have mentioned, it should give you a good idea of why the probe can go into alarm mode.

BLTouch Blinking Red Slowly

The second BLTouch red LED pattern that shows us that the probe is experiencing an error is the red LED flashing slowly, where it is on for 80% of the flashing cycle.

A slowly flashing red LED on the BLTouch shows us that a problem exists with either the GND (ground) or the +5V (power) wires.

Here are some of the factors that can cause a problem with the GND and +5V wires and trigger the red LED blink:

  • Reversed +5V wire (the most common culprit)
  • Faulty connection between the wire and the board
  • Wire damage
  • Pin damage

Note that while the BLTouch may still work in this state, the best course of action is to find the source of the problem and fix it before using the probe again to prevent issues from appearing down the line.

How Can I Fix BLTouch Blinking Red?

As the BLTouch can blink red in two different ways, the most vital part of the fixing process is to recognize the pattern to ensure that you apply the correct solution.

Fixing BLTouch Blinking Red Slowly

While a few different factors can cause the BLTouch to blink red slowly, the fix is usually simple.

To fix the issue of BLTouch blinking red slowly, we recommend following the steps below:

  1. Ensure that the pin can move in and out freely and clean up any dust or dirt that may obstruct it.
  2. Raise the printhead to prevent the pin from hitting the build plate.
  3. Increase the Z-axis homing speed.
  4. Re-flash the firmware.

More often than not, the steps above should get your BLTouch in working order.

If you still experience the same issue after following the steps above, we recommend replacing the BLTouch due to the possibility of the probe being damaged is high.

Fixing BLTouch Blinking Red Quickly

Since we know that BLTouch blinking red quickly is wire-related – following a simple checklist will do the job unless the wires are permanently damaged.

Here are the solutions we recommend for fixing the issue of BLTouch blinking red quickly:

  • Double-check the wires and ensure that the headers are aligned correctly (not reversed).
  • Ensure that the pins on the board are clean.
  • Ensure that the header sits tightly on the pins and doesn’t wobble.

As there are many cases where users report that the wires of the BLTouch are in reverse order, ensure that the colors of the wires are in the correct order instead of assuming that the front side of the header is automatically the right choice.

You can get more information about the color scheme of the wiring here.

Why Is My BLTouch’s Red LED Always On?

Another light pattern we can observe on your BLTouch is the red LED always being on, with the red color often causing the users to feel that something is wrong.

The red LED on the BLTouch being always on means that the probe is operating without any issues.

As the only two error codes that involve the red LED are when it flashes slowly or quickly, there is no need to be concerned if the red LED is always on or always off.

If you would like to learn more about the flashing patterns of the LEDs and what they signify, you can refer to the BLTouch manual.

Wrapping Up

While seeing your BLTouch blink red can be disappointing, especially if you have installed it for the first time, it’s an issue that you shouldn’t worry too much about as it is pretty straightforward to solve in most scenarios.

To quickly summarize, the BLTouch red LED can blink in two different ways, with both referring to separate issues.

While a quick blinking red LED indicates that the BLTouch is in alarm mode, which signifies that it has failed the self-test (can be many reasons behind it, such as obstruction of the pin), a slow blinking red LED refers to issues with either the GND or the 5V wire.

Happy printing!