Prusa error 13205 (Bed Maxtemp Error) appears on the MK4 and surfaces as #26205 on the MK4S, #21205 on the MK3.9, and #23205 on the MK3.5. The firmware detected that the heatbed thermistor is reporting a temperature above the safe upper limit, triggering an immediate halt to prevent a thermal runaway event or damage to the bed hardware.

What the Error Means

The bed thermistor continuously feeds temperature data to the Buddy board. If the reported value exceeds the configured maximum threshold, the printer assumes one of two failure modes: the thermistor circuit has shorted, causing it to report an artificially high reading, or the bed is genuinely overheating due to a runaway heating condition. Both scenarios require the printer to stop immediately. A shorted thermistor connector or damaged wiring is the most common cause — the thermistor itself rarely fails in a way that produces a high reading without a wiring fault contributing.

Step-by-Step Fix

1. Power off and let the printer cool completely. Never work on thermistor wiring while the bed or electronics are warm. Give the printer at least 15 minutes before touching any components.
2. Inspect the heatbed thermistor cable. Trace the thin two-wire thermistor cable from the heatbed underside to its connector on the xBuddy board. Look for pinched sections, bare wire touching metal, or melted insulation — any of these can cause a short that reads as a falsely high temperature.
3. Check for bridging at the thermistor contacts. Examine the small thermistor bead on the underside of the heatbed. Make sure the Kapton tape holding it flat has not shifted, exposing both contacts simultaneously to a conductive surface.
4. Reconnect the thermistor connector on the xBuddy board. Unplug the connector, visually inspect the pins for damage or contamination, and firmly reseat it.
5. Measure thermistor resistance with a multimeter. Disconnect the thermistor connector and measure across the two pins. At room temperature (approximately 20–25°C) an NTC 100k thermistor should read approximately 85–110 kΩ. A reading near zero indicates a short; replace the thermistor cable if so.
6. Replace the heatbed thermistor cable if shorted. Use the official Prusa spare part and route the replacement cable identically to the original.

Parts Required

• Replacement NTC 100k heatbed thermistor cable (if shorted or damaged)
• Kapton tape (to re-secure thermistor bead if adhesive has failed)
• Digital multimeter

If the error returns after replacing the thermistor, contact Prusa Support at help.prusa3d.com — persistent Maxtemp faults can indicate an xBuddy board issue.

Frequently asked questions

What does Prusa 13205 mean?

Prusa error 13205 (Bed Maxtemp Error) appears on the MK4 and surfaces as #26205 on the MK4S, #21205 on the MK3.9, and #23205 on the MK3.5. The firmware detected that the heatbed thermistor is reporting a temperature above the safe upper limit, triggering an immediate halt to prevent a thermal runaway event or damage to the bed hardware.

How do I fix Prusa 13205?

Prusa error 13205 means the heatbed thermistor read above the safe upper limit. Learn how to identify a shorted thermistor, damaged wiring, or runaway condition.