Why does my ESP8266 keep restarting?

Question

I just got a brand new ESP8266 and tried uploading a basic sketch (just a simple Serial.begin() and a few prints), but as soon as it runs, the board keeps restarting in a loop.

I haven’t connected any sensors or peripherals — just powered it via USB. The Serial Monitor keeps showing reset messages like rst cause: 4 or something similar.

Is this normal for a new board? Could it be a power issue, bad code, or something else I’m missing?
Would really appreciate any suggestions before I start panicking

Jignesh · Answer

There are a few common reasons why your ESP8266 keeps restarting:

Power supply issue –

This is the most common cause. The ESP8266 needs a stable 3.3V with enough current (at least 300mA, preferably 500mA). If you're powering it from the 3.3V pin on an Arduino or a weak USB cable, that could cause resets.

Watchdog reset –

If your code runs a long loop without delay(), yield(), or ESP.wdtFeed(), the internal watchdog timer will reset the ESP. Try adding a small delay(1) inside long loops.

Incorrect GPIO boot states –

The ESP8266 checks GPIO0, GPIO2, and GPIO15 at boot. They need to be:

1. GPIO0: HIGH

2. GPIO2: HIGH

3. GPIO15: LOW

If these are wrong, the ESP may not boot properly and keeps resetting.

Faulty code or firmware –

A crash or corrupt firmware can cause repeated resets. Try uploading a basic sketch (like Blink) to rule that out.

Serial monitor clues –

Connect your ESP to the serial monitor at 74880 or 115200 baud. The output usually shows the reset cause. For example:

rst cause:2 = reset from RST pin

rst cause:4 = watchdog reset

Wi-Fi reconnect loop –

If your code keeps trying to connect to Wi-Fi and fails (especially without any delay), it can cause instability.

Double-check your power supply first — it's usually the culprit. If you're still stuck, share your wiring setup and what shows up in the serial monitor.