Why Xiaomi Redmi Note 9 is constantly rebooting and how to fix it

Your Xiaomi Redmi Note 9 suddenly started to reboot for no apparent reason? This is one of the most common problems for owners of this model, and it can manifest itself in various ways, from random reboots once an hour to complete inability to boot the system. The reasons range from software failures to hardware malfunctions, and without proper diagnosis you risk wasting time on useless manipulations.

In this article, we will look at all the possible causes of cyclical reboot, from trivial overheating to damage to the motherboard, you will receive step-by-step instructions with photos and videos that will help bring your smartphone back to life, and also learn when to contact the service center, and pay special attention to the hidden settings of MIUI, which are often overlooked even by experienced users.

Before you start repairing, answer one question: after what event did the reboot begin?

1. Diagnostics of the problem: software failure or hardware malfunction?

The first thing you need to do is to determine if the problem is software or hardware, which will save you hours of useless manipulation, and here are the key signs of each type of malfunction:

• 🔄 Software glitch: phone reboots on logo MI, but sometimes still loads; crashes started after updating or installing the application; c Settings → There's an error message on the phone.
• 🔧 Hardware problem: reboots occur when heating, vibrating or charging; phone turns off with a characteristic click; artifacts appear on the screen before reboot.
• 🔋 Battery problems: smartphone reboots at charge level below 30%; battery swells (see above the raised screen); phone shuts down even at 50% charge.

If you see a combination of several signs (e.g. overheating + turning off when charging), the problem is likely complex, in which case start with the simplest solutions and gradually move on to radical ones.

For accurate diagnosis, use the Fastboot mode:

1. Turn off your phone (if possible).
2. Press the Power button + Volume down for 10 seconds.
3. If the phone loads in Fastboot Mode, it's software problem. If it doesn't (the screen is black or flashing), it's hardware.

2. Software solutions: from cache reset to flashing

In 60 percent of cases, Redmi Note 9 cyclical reboots are caused by firmware failures or application conflicts. Start with the safest methods and move to the more radical ones.

2.1 Clearing the cache through Recovery

This is the first step that won't delete your data, but it can solve the problem if it's related to corrupted temporary files.

If the cache is cleaned, then you can move on to the next step, and note that you don't confuse Wipe Cache with Wipe Data, because the second option will delete all your data!

Reset to factory settings

If the cache cleanup didn't work, you'll have to take more serious steps. SIM-map SD-card (if any).

Method 1: Menu (if the phone is sometimes loaded):

1. Go to Settings → About the phone → Reset settings.
2. Choose to erase all data.
3. Enter your password (if required) and confirm.

Method 2: Recovery (if the phone doesn't boot):

1. Press Power + Volume up to enter Recovery.
2. Choose Wipe Data → Wipe All Data.
3. Confirm the action and wait for the completion.

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If after resetting the phone requires a Mi Account that you do not remember, use the official Mi Unlock tool (it will require a linked phone number).

2.3 Fastboot flashing

If the reset didn't work, the last software method is complete firmware, and you'll need a computer and an original computer. USB-cable.

Step-by-step:

1. Download the official firmware for the Redmi Note 9 (code model merlin).
2. Unpack the archive and install the Mi Flash Tool drivers.
3. Connect your phone in Fastboot mode (clip Power + Volume down).
4. Run MiFlash.exe, select the firmware folder and click Refresh → Flash.

It takes 5-10 minutes. Don't turn off your phone until you have a green checkmark in the program. Once you flash it, the phone automatically restarts.

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Fastboot flashing removes all data, including Mi Account blocking, and only use this method if other methods have not worked.

3. Hardware causes: battery, plumes, motherboard

If the software methods didn't work, the problem is the hardware. The Redmi Note 9 has a few hardware malfunctions leading to cyclical reboots:

• 🔋 Bloated battery – presses on the motherboard, causing short circuits.
• 🔌 Oxidized contacts of the charging port or battery.
• 📱 Disconnected display plume or power buttons.
• 🔥 Overheating of the processor due to dried thermal paste.
• 🛠️ Damage to the motherboard (often after falls or moisture hits).

You can only check the battery and contacts yourself, and the rest of the problems will require disassembly of the phone and diagnostic equipment.

Replacement of the battery

If the phone reboots at a charge level below 30% or the body is blown up, the battery must be replaced. For the Redmi Note 9, a 5020 mAh battery labeled BM4B is suitable.

Step-by-step replacement instructions:

1. Turn off the phone and remove it. SIM-map.
2. Heat the back cover with a hair dryer (60-70°C) and tuck it with a plastic spatula.
3. Unplug the battery by putting it under special tongues (do not pierce!).
4. Disconnect the battery plume and install a new one.

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Stick the new battery onto the 3M 9448A double-sided tape, which provides better thermal conductivity and prevents bloating.

Cleaning of contacts and charging port

Oxidized contacts can cause false alarms of the charging sensor, which leads to sudden reboots.

• Use alcohol (90%+) and cotton swab to clean the battery contacts.
• A toothpick will be suitable for the charging port (remove the dirt carefully).
• Blow the port with compressed air (a canister for cleaning equipment).

If the problem remains after cleaning, check the cable and power supply - unoriginal accessories often cause voltage surges.

4.Overheating: Why the Redmi Note 9 shuts down from high temperature

The MediaTek Helio G85 processor in the Redmi Note 9 is prone to overheating, especially under intense loads (games, 4K video shooting). If the phone reboots when it is warmer than 50°C, follow these recommendations:

• 🎮 Limit it. FPS in games through graphics settings (maximum 60) FPS).
• ☀️ Avoid direct sunlight – even in standby mode, the phone can overheat.
• 🧊 Remove the case while charging or playing.
• 🔄 Update the firmware - in new versions MIUI Optimized cooling system.

To check the temperature, use the AIDA64 app (Sensors section).

If the CPU temperature exceeds 70°C in simple tasks (video viewing, messengers), this indicates a dried thermal paste or a malfunction of the cooling system, in which case disassembly and replacement of the thermal interface are required.

5. Problems after the MIUI update: rollback and alternative firmware

Many users experience cyclical reboots immediately after the MIUI update, due to errors in new firmware versions or incompatibility with modified components (such as custom recavery).

Here's what we can do:

• 🔙 Reverse to the previous version via Mi Flash Tool (download the old firmware from xiaomifirmwareupdater.com).
• 🛠️ Install custom firmware (e.g. Pixel Experience or LineageOS) – requires an unlocked bootloader.
• 🔧 Manual installation of patches through TWRP (If the phone is loaded into the recavator).

To revert to the previous version of MIUI:

1. Download the archive with firmware (e.g. MIUI 12.5.3 for Redmi Note 9).
2. Connect your phone in Fastboot mode.
3. In the Mi Flash Tool, select the clean all and lock option (this will block the bootloader back).

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Before installing custom firmware, check compatibility with the merlin model (code Redmi Note 9). Incompatible firmware can "brick" the phone.

6. When to contact the service center?

If you’ve tried all the techniques in this article, but the Redmi Note 9 is still rebooting, the problem is likely hardware and requires professional repair.

• 💥 Phone does not turn on at all (black screen, no reaction to charging).
• 🔥 On the motherboard, blackened or bloated elements are visible.
• 💧 The phone was in the water (even if it worked normally).
• 🛠️ After the fall, cracks appeared on the board (see when disassembling).

The cost of repairs in Xiaomi service centers:

Before visiting the service, back up your data (if the phone is switched on sometimes) and remove all locks (PIN, pattern lock, Mi Account) to speed up the repair process.

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Xiaomi's official service centers offer a 6-12 month warranty, and informal workshops can offer cheaper, but without warranties.

7.Prevention: How to Prevent Reboots in the Future

To avoid repeated issues with the Redmi Note 9, follow these guidelines:

• 🔋 Charge your phone with the original cable (current 2A, voltage 5V).
• 📱 Do not install applications from unknown sources – they may contain malfunctioning viruses.
• 🔄 Update. MIUI regularly, but don’t put bat versions (they often contain bugs).
• 🧹 Clean the cache once a month through Settings → Warehouse → Clear the cache.
• 🛡️ Use a case with shock protection – even a small drop can damage the fee.

It is also worth turning off automatic MIUI optimization, which sometimes conflicts with background processes:

1. Go to Settings → Battery and Performance.
2. Turn off the Adaptive Charging option.
3. In the Optimization section, select Manual Setup.

FAQ: Frequent questions about Redmi Note 9 reboots