Prusa error 13506 (ESP Error — WiFi Fault) appears on the MK4 and its equivalents are #31506 on the CORE One, #35506 on the CORE One L, #26506 on the MK4S, #27506 on the MK3.9S, #21506 on the MK3.9, #28506 on the MK3.5S, and #23506 on the MK3.5. Unlike error 13505 which occurs at startup, this fault fires during active operation — the ESP32 Wi-Fi module was running normally and then encountered a fault that caused it to crash or disconnect mid-session.

What the Error Means

The ESP32 module handles all Wi-Fi communication between the printer and Prusa Connect. An in-session ESP fault typically means the module received a command it could not process, lost its connection to the xBuddy board host, or encountered an internal watchdog timeout. A weak or congested Wi-Fi signal can also cause the module to repeatedly attempt reconnections, eventually exhausting internal buffers and crashing. This error does not affect local USB printing, but Prusa Connect monitoring and remote control will be unavailable until the module recovers.

Step-by-Step Fix

1. Restart the printer to reset the ESP module. Most mid-session ESP faults clear on reboot and do not repeat. Power off, wait 10 seconds, and power back on.
2. Re-establish the Wi-Fi connection. After restarting, navigate to LCD Menu → Settings → Network and confirm the printer reconnects to your Wi-Fi network.
3. Check the ESP antenna cable. The ESP32 module has a small flexible antenna attached via a U.FL or similar micro connector. With the printer off, confirm the antenna connector is firmly seated on the module and the antenna cable is not damaged or pinched.
4. Move the printer closer to the Wi-Fi router if signal is weak. A weak signal causes the ESP32 to work harder, increasing the probability of a fault condition. You can view signal strength in the printer’s network settings menu.
5. Update firmware. Printer firmware updates include updated ESP32 firmware which often resolves stability issues. Download the latest from prusa3d.com/drivers and install via USB.
6. Contact Prusa Support if faults repeat consistently across restarts. If the module crashes every session or within minutes of each restart, the ESP module may need replacement.

Parts Required

• No replacement parts are typically required for this fix — basic tools only
• Replacement ESP32 Wi-Fi module (if the module is confirmed faulty — contact Prusa Support first)

If the fault recurs across multiple firmware versions, contact Prusa Support at help.prusa3d.com with the exact firmware version and a description of when the fault occurs.

Frequently asked questions

What does Prusa 13506 mean?

Prusa error 13506 (ESP Error — WiFi Fault) appears on the MK4 and its equivalents are #31506 on the CORE One, #35506 on the CORE One L, #26506 on the MK4S, #27506 on the MK3.9S, #21506 on the MK3.9, #28506 on the MK3.5S, and #23506 on the MK3.5. Unlike error 13505 which occurs at startup, this fault fires during active operation — the ESP32 Wi-Fi module was running normally and then encountered a fault that caused it to crash or disconnect mid-session.

How do I fix Prusa 13506?

Prusa error 13506 means the ESP32 Wi-Fi module crashed during operation. Learn how to restart, update firmware, and check the antenna to restore network connectivity.