5 Causes for a Raspberry Pi That Won’t Boot (And How to Fix Them)

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You’ve got your Raspberry Pi all hooked up, ready to run… but when you connect the power, nothing happens. Something, somewhere is wrong, but what? And what can you do about it?

Here are five things to check if you need to troubleshoot a Raspberry Pi that should be working but for some reason won’t boot.

1. Make Sure It Isn’t Booting, Check the LEDs

When a Raspberry Pi boots, one or more LEDs will activate. One is red, indicating power (PWR); the other is green, and indicates activity (ACT). (There is also a trio of LEDs indicating the Ethernet status, if connected.)

Raspberry Pi Model B

So what do these LEDs indicate? Well, there’s the normal status, which is both PWR and ACT LEDs activated. ACT will flash during SD card activity, while PWR blinks when power drops below 4.65V. As such, if the red PWR LED doesn’t light up, there’s no power.

If only the red PWR LED is active, and there is no flashing, then the Pi is receiving power, but there is no readable boot instruction on the SD card (if present). On a Raspberry Pi 2, ACT and PWR LEDs lit up means the same.

When booting from an SD card, the ACT light should have an irregular blink. However, it can blink in a more regulated manner to indicate a problem:

  • 3 flashes: start.elf not found
  • 4 flashes: start.elf cannot launch, so it’s probably corrupt. Alternatively, the card is not correctly inserted, or card slot is not working.
  • 7 flashes: kernel.img not found
  • 8 flashes: SDRAM not recognized. In this case, your SDRAM is probably damaged, or the bootcode.bin orstart.elf cannot be read.

If any of these indicators occur, try a fresh SD card with a newly installed Raspberry Pi operating system. No joy? Scroll down to check what the problem could be.

2. Is the Power Adapter Good Enough?

As noted above, power issues can cause a Raspberry Pi to fail. It might switch off or hang when running, or it might simply fail to boot at all. This is because a stable power supply unit (PSU) is required for the SD card to be reliably read.

To ensure your PSU is good enough, check that it meets the specification of your particular Raspberry Pi model. Similarly, confirm that the micro-USB from the PSU to the Pi is up to scratch. A lot of people use smartphone chargers to power their Raspberry Pis. This usually isn’t the best idea; a dedicated, suitable PSU is the preferred approach.

The Raspberry Pi has a resettable fuse. This polyfuse can reset itself, but it can take up to a couple of days. If you have accidentally blown the polyfuse, you’ll only find out when you try booting later on. It’s worth using the intervening time to buy a suitable Raspberry Pi PSU, such as the CanaKit 5V 2.5A Adapter on Amazon.




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3. Is the Operating System Installed?

Your Raspberry Pi will not boot if there is no operating system installed and it lacks a boot script that lets you install an OS (such as NOOBS or BerryBoot).

As such, if there is no OS installed on the SD card, you’ll get no joy from your Raspberry Pi. Deal with this by ensuring an OS is available. Install Raspbian (or Raspbian Lite if you’re short of time), or use NOOBS to get the Pi up and running and choose an OS to download and install.

4. Confirm the microSD Card Works

A working Raspberry Pi will rely on a good quality SD card for booting, and usually running the OS (although later models can subsequently boot from USB devices). If the SD card isn’t working, then your Raspberry Pi will be erratic, or simply fail to boot.

SD cards should be formatted before use.

Start by checking the card works. You can do this by powering down the Pi, and inserting the SD card into your PC. Use a reliable flash drive formatting tool, and attempt to reformat (on Windows and Mac, use the SDFormatter tool from the SD Association). If formatting fails, then the card is corrupt (SD cards from SanDisk can be returned under warranty).

When setting up a new Raspberry Pi OS, it’s always best to format the SD card prior to writing the image. This means using a reliable card reader/writer, as well as suitable media. Look for media with a high write speed, too, and superior error checking, to ensure a fast, efficient Raspberry Pi.

Only buy SD cards from reputable suppliers, such as this Sandisk 64GB microSD Card on Amazon. Other reputable brands include Samsung and PNY, both of which can also be found on Amazon.




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5. No Video Output?

Your Raspberry Pi cannot display any video without an SD card present. There is no on-board BIOS, so there’s no way anything can be displayed. Therefore, you need to ensure that you’re using a reliable, working HDMI cable.

Meanwhile, the Pi itself needs to detect the display. Similarly, the display device needs to be capable of detecting the signal from the Raspberry Pi. If the Pi appears to be failing to boot because nothing appears on screen, you’ll need to force HDMI detection.

You can do this on your computer by inserting the SD card, and browsing to the /boot/ partition. Open the config.txt file, and add the following to the end:

hdmi_force_hotplug=1

Save and exit the file, safely remove the SD card, return it to your Raspberry Pi, then try to power up again.

Meanwhile, if you’re using NOOBS with the aim of installing an operating system on your Raspberry Pi, and nothing appears on the display, you can try some keyboard shortcuts. Within the first ten seconds of booting, tapping 1, 2, 3, and 4 on your keyboard will force the display output signal to switch between ideal HDMI, safe HDMI, PAL composite, and NTSC composite.

Other video options are also possible. However, recent Pi models use TRRS, which means you need the correct cable, one capable of translating the RCA (red and white connectors) and composite (yellow connector) signals.

You can find a suitable TRRS A/V Cable on Amazon. This should work for you if HDMI is not an option.




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How to Spot a Dead or Defective Raspberry Pi

If you’ve got this far with no results, then there is a chance that your Raspberry Pi is defective. The chances of this are slim, as they’re all tested following manufacture.

A Raspberry Pi Zero

For a Raspberry Pi B, B , 2B, 3B, or 3B (what are the differences between Raspberry Pi boards?), the only way to work out if it is broken is to have an identical model to hand, one that you know is working. From the suspect device, remove the SD card, Ethernet cable, power lead, and HDMI cable—and anything else that is connected—and substitute the working device with the same cables, peripherals, and SD card.

If the device boots, your other Pi is faulty; if not, then your cables, power supply, or SD card are causing the problem. See above.

Meanwhile, for Raspberry Pi A, A , and Zero devices, there is different way to check suspect devices. Remove all cables, and the SD card, and connect the device via USB cable to your Windows PC (USB-A to USB-A for the Raspberry Pi A and A , micro-USB to USB-A for the Pi Zero models).

If working, the device will be detected, and an alert will sound, and you’ll find the Raspberry Pi listed in Device Manager as “BCM2708 Boot”. On Linux and Mac, you’ll find a working Raspberry Pi A or Zero listed in response to the dmesg command in the terminal.

Raspberry Pis have a 12-month warranty, but don’t return it without first checking the terms and conditions.

Raspberry Pi Boot Problems: Fixed!

So, that’s five things you need to check to fix Raspberry Pi boot issues. Here’s a recap:

  1. Check the LEDs
  2. Is the power adapter suitable?
  3. Have you installed the operating system?
  4. Is the microSD card reliable?
  5. Is HDMI output disabled?

Meanwhile, if your Raspberry Pi is one of the few that are genuinely defective, use the steps above to confirm this.

Managed to get everything up and running? Great! Now take a look at these awesome Raspberry Pi projects to get started.

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