> ## Knowledge Base Index
> Fetch the complete knowledge base index at: https://help.simplyprint.io/sitemap.xml
> Use this file to discover available pages before exploring further.
> Pure-Markdown content can be obtained by appending a '.md' suffix to the content URLs listed in the sitemap (without the trailing slash).

# Why does my OctoPrint printer show as "Not connected"?

# Why does my OctoPrint printer show as "Not connected"?

## TL;DR

**Your printer can't talk to OctoPrint over USB. SimplyPrint just reports what OctoPrint reports - we can see that the connection isn't happening, but the fix is not on our side.** Almost always it's the USB cable, USB power, the printer firmware, or a printer-specific quirk OctoPrint needs help with. The fastest path to a fix:

1. **Open OctoPrint directly** at `http://<pi-ip-address>` and read the **Connection panel** + **Terminal tab**. That's where the actual error lives.
2. Try a different **data-grade** USB cable.
3. If you're running an Anycubic, Creality, Anet, or a printer with a finicky USB board, see [printer-specific quirks](#5-printer-specific-quirks-and-octoprint-plugins) below.
4. If you've worked through this article and it still won't connect, the best places for help are **the OctoPrint Community forum** ([community.octoprint.org](https://community.octoprint.org)) and the **OctoPrint Discord** - they have far more eyes on this layer of the stack than SimplyPrint support does.

||| **This is not a SimplyPrint bug, and SimplyPrint support can't fix it.** "Not connected" means OctoPrint itself cannot reach your printer over the USB cable. SimplyPrint mirrors OctoPrint's connection state: if OctoPrint can't connect, neither can SimplyPrint. The fix is between OctoPrint, the Pi, the USB cable, and the printer - all layers we don't control. We can point you at the right diagnostics, but the actual fix happens on your side.

## 1. Step 1: Open OctoPrint directly

Before anything else, open OctoPrint in your browser at `http://<pi-ip-address>` (or whatever address you set up). OctoPrint will tell you exactly what's failing, because it's the layer talking to the serial port.

**Read these in OctoPrint:**

| Where | What it tells you |
| --- | --- |
| **Connection panel** (top left) | The serial port, baud rate, and the exact error. Common ones: "No serial port found", "Connection error", "Failed to autodetect baudrate". |
| **Terminal tab** | What the printer is (or isn't) sending. An empty terminal means nothing's coming through the cable. Garbled text means baud rate is wrong. |
| **State** | If it says "Offline" or "Closed" here too, the issue is confirmed to be below OctoPrint - not SimplyPrint. |

> If OctoPrint **can** connect to the printer but SimplyPrint still shows "Not connected", that's a different problem - see [Why is my OctoPrint-powered printer offline?](https://help.simplyprint.io/en/article/why-is-my-octoprint-powered-printer-offline-1rqmxh9/) instead.

## 2. Quick checklist

1. Is the printer powered on?
2. Try a different USB cable - it must be a **data cable**, not charge-only (more on this below).
3. Try a different USB port on the Pi.
4. Power-cycle the printer (off, wait 30 seconds, on).
5. Restart the Pi.

If none of that fixed it, read on.

## 3. Bad USB cable (about 9 out of 10 cases)

Many USB cables are charge-only and can't transmit data. They look identical to data cables from the outside.

**Signs of a bad cable:**
- Very thin, no shielding
- Bundled with a phone charger or budget gadget
- No markings or branding
- You've had flaky behaviour with it before

**Fix:** A known-good shielded USB cable, preferably with ferrite cores (the cylindrical bumps near the ends) which reduce interference from the printer's stepper motors.

Reference: [Which cable to use for SimplyPrint / OctoPrint](https://help.simplyprint.io/en/article/which-cable-to-use-for-simplyprint-octoprint-a31397/)

## 4. USB power: backpowering and undervoltage

This is a real, well-documented issue with some printers. Worth knowing about because it produces the exact same "Not connected" symptom **and** random Pi reboots / undervoltage warnings.

### What backpowering is

On certain printer mainboards (older Creality Ender 3 boards, Anet A8, Anycubic Mega, and others), the 5V rail on the USB port is tied to the mainboard's 5V supply. When connected to a Pi:

- The Pi can feed power **into** the printer mainboard - keeping the printer's LCD lit even when the printer is "off"
- The printer mainboard can feed power **back into** the Pi - causing undervoltage detection, random reboots, and dropped USB connections mid-print

Either direction causes the same end result for you: "Not connected" in OctoPrint, intermittently.

### Symptoms

- Printer LCD stays on when the printer power supply is switched off
- Lightning-bolt undervoltage icon in OctoPrint's top bar
- Pi randomly reboots, especially when the printer's heated bed or hotend turns on
- Connection drops mid-print

### Fixes (best to worst)

1. **USB isolator** (best). A hardware device sitting between Pi and printer that electrically isolates the two sides. About $20.
2. **Powered USB hub** between Pi and printer. Cheaper, works well, and also gives you more ports.
3. **Tape over the USB +5V pin** on the cable (pin 1 on the Pi side). A common community fix - blocks power transfer without affecting data. Some sellers also list "data-only" cables that have this done for you.
4. **Power-on sequence:** turn the printer on *first*, then connect the USB cable. Helps in mild cases.
5. **Better Pi power supply** (5.25V / 3A+ official Raspberry Pi supply) if undervoltage is your symptom. Doesn't fix backpowering, but increases margin.

> Don't use a phone charger to power the Pi. They almost always trigger undervoltage under load.

Background reading: [OctoPrint Community: printers known to have backpowering issues](https://community.octoprint.org/t/printers-known-to-have-backpowering-issues-new-solution/44754).

## 5. Printer-specific quirks and OctoPrint plugins

Some printers don't speak the standard Marlin protocol cleanly, and OctoPrint can struggle to autodetect or stay connected without a printer-specific plugin or manual baud rate. **This is something the OctoPrint Community has documented extensively per printer model** - if you've tried the steps above and you have one of these printers, search the OctoPrint forum for your printer model.

| Printer family | Common quirk | Typical fix |
| --- | --- | --- |
| **Anycubic i3 Mega / Mega S** | Non-standard `M115` / `OK` responses; baud rate autodetect fails | Manually set baud to **250000** in OctoPrint; install a community Anycubic-specific plugin if available |
| **Creality Ender 3 / CR-10 (older boards)** | Default baud is 115200, newer "silent" boards use 250000 | Manually set baud; older boards sometimes need a specific cable to pass through the USB filter on the board |
| **Anet A8 / clones** | Custom serial config, sometimes needs Marlin reflash | Community forum has model-specific guides |
| **Prusa MK3 / MK3S / MK3S+ / MK3.5 / MK3.9** | "RPi port" setting on the printer disables the regular USB port | On the printer: Settings > **RPi port** > **off**. ![How to disable the RPi port setting on a Prusa MK3](https://cdn.simplyprint.io/i/static/connectissue/prusa-no-connect.gif?v=3) |

If `Autodetect baudrate` is failing in OctoPrint, **don't keep retrying it**. Set the baud manually. Try **250000** first, then **115200**, then **230400**.

## 6. Bad printer mainboard (rare)

Rare but real, especially after a failed firmware flash or a USB port that's been physically stressed. If you've ruled out everything above and the printer's USB port still doesn't respond, the mainboard may need replacing.

**Quick test:** plug the same cable into a different printer using the same Pi. If that one connects fine, your original printer's mainboard is the suspect.

## 7. Wrong setup guide (no USB port on the printer?)

||| **Cable can't fit your printer? You're probably using the wrong setup guide.**

OctoPrint is for **Marlin-based printers** that connect to a Raspberry Pi over USB. If your printer:

- Runs Klipper natively (most modern Creality K1/K2, Elegoo Centauri, etc.)
- Doesn't have a USB-B / Mini USB / USB-C port for printer connection
- Is a Bambu Lab, Prusa with built-in WiFi (MK4 / XL / Core One), or an Ultimaker

...then OctoPrint is the wrong setup path. Pick the correct one at [simplyprint.io/setup-guide](https://simplyprint.io/setup-guide).

**Quick firmware test:** look at the menu on your printer screen. If the menu looks like a typical Marlin LCD (text-only, brand-neutral options), OctoPrint is the right path. If it's a custom UI (Klipper screens like KlipperScreen, or brand-specific UIs like Bambu's), use the recommended setup for that brand instead.

## Still stuck? Where to get help

We mean this honestly: **the OctoPrint community is the right place for this**, not SimplyPrint support.

- **OctoPrint Community forum** - [community.octoprint.org](https://community.octoprint.org). Searchable, deep, model-specific archives. The answer to your problem is probably already there.
- **OctoPrint Discord** - linked from the OctoPrint Community forum. Faster for back-and-forth diagnosis.
- **SimplyPrint Discord** - [simplyprint.io/discord](https://simplyprint.io/discord). Good if you want a second pair of eyes from us, but understand that for cable / power / firmware / plugin issues we're going to point you back to OctoPrint anyway.

If you do post for help anywhere, **include a screenshot of the OctoPrint Connection panel + Terminal tab**. That single screenshot will get you a faster, better answer than any description of the symptom.

---

## Related articles

- [Why does my printer show as "Not connected"?](https://help.simplyprint.io/en/article/why-does-my-printer-show-as-not-connected-m5gdmh/)
- [Why is my OctoPrint-powered printer offline?](https://help.simplyprint.io/en/article/why-is-my-octoprint-powered-printer-offline-1rqmxh9/)
- [Which cable to use for SimplyPrint / OctoPrint](https://help.simplyprint.io/en/article/which-cable-to-use-for-simplyprint-octoprint-a31397/)
- [Pick the right Raspberry Pi](https://help.simplyprint.io/en/article/pick-the-right-raspberry-pi-for-running-simplyprint-octoprint-2wj57s/)
- [Prusa printer keeps disconnecting](https://help.simplyprint.io/en/article/prusa-printer-keeps-disconnecting-from-simplyprint-octoprint-or-wont-connect-prazhj/)