Prusa error 13309 (Heatbed Port Overcurrent) appears on the MK4 and its equivalents are #31309 on the CORE One, #35309 on the CORE One L, #26309 on the MK4S, #27309 on the MK3.9S, #21309 on the MK3.9, #28309 on the MK3.5S, #23309 on the MK3.5, and #12309 on the MINI. The xBuddy board detected that current to the heatbed exceeded safe limits and stopped the printer to protect the electronics.

What the Error Means

The heatbed draws significantly more current than the hotend heater — typically 10–15 A depending on the bed size and voltage. The xBuddy board’s bed port is protected by overcurrent monitoring. If the heatbed power cable is damaged and two conductors are partially touching, or if a connector has loosened and is creating a resistive arc, the current profile becomes abnormal and trips this fault. Burn marks on the xBuddy board’s bed connector are a tell-tale sign of a connector that has been running hot from loose contact.

Step-by-Step Fix

1. Turn off the printer and let it cool. The bed and electronics can remain hot for several minutes — give the printer time to cool before working on any connections.
2. Trace the heatbed power cable for damage. Follow the thick two-conductor cable from the underside of the heatbed to the xBuddy board. Look for cuts, pinched sections, frayed insulation, or burn marks along the cable length.
3. Reconnect all heatbed connectors. Unplug and firmly reseat the heatbed power connector at the underside of the bed and at the xBuddy board. A loose connection increases resistance, causes heating at the connector, and can trigger overcurrent faults.
4. Examine the xBuddy board bed connector for burn marks or bent pins. Open the electronics enclosure and inspect the board-side connector carefully. Discoloration or melted plastic around the pins indicates the connector has been arcing and needs replacement.
5. Measure the heatbed resistance. With the bed cable fully disconnected, measure resistance across the heatbed power terminals. A typical 24V MK4 heatbed reads approximately 1.5–2 Ω. A reading significantly lower than expected suggests a fault within the bed heater itself.
6. Replace damaged components. Replace the heatbed cable if damaged; contact Prusa Support if the xBuddy board connector shows burn damage requiring board replacement.

Parts Required

• Replacement heatbed power cable (if cable shows damage or burn marks)
• Replacement xBuddy board (if connector is burned — contact Prusa Support first)
• Digital multimeter

If the board-side connector shows burn damage, contact Prusa Support at help.prusa3d.com before powering the printer on again.

Frequently asked questions

What does Prusa 13309 mean?

Prusa error 13309 (Heatbed Port Overcurrent) appears on the MK4 and its equivalents are #31309 on the CORE One, #35309 on the CORE One L, #26309 on the MK4S, #27309 on the MK3.9S, #21309 on the MK3.9, #28309 on the MK3.5S, #23309 on the MK3.5, and #12309 on the MINI. The xBuddy board detected that current to the heatbed exceeded safe limits and stopped the printer to protect the electronics.

How do I fix Prusa 13309?

Prusa error 13309 means an overcurrent fault occurred on the bed heater port. Learn how to inspect the heatbed cable and xBuddy board connections to restore safe operation.