Heatbed not heating up properly

Updated 2 days ago ​by Tomáš Chvalina

If your Heatbed does not heat up. There are a couple of things we can check to diagnose the source of the issue.

So please check following common issues: 

  1. Visually check that your Heated bed is not badly damaged or does not have exposed traces (photo n.1)
  2. Check out that your Heated bed thermistor is properly attached under the Golden Kapton tape (photo n.2 & 3)
  3. Loosen Heated bed connectors on the miniRAMBO board. Simply open the miniRAMBO box and un-plug and re-plug the connector. 

Photo 1


Photo 2 & 3

                                                                   Not the two types of tape securing the thermistor. There is a layer of aluminum foil tape underneath the layer of kapton tape.      

                                                                    Loose thermistor

If you notice the thermistor is hanging freely, unattached to the bed, undo the 6 bolts holding the bed to the Y carriage and re-secure the thermistor.

If none of the above helped. Please follow the instructions bellow for less common cases.

Heatbed Heater vs. Thermistor test

The best and easiest way is to take a hair dryer and blow hot air at the Heatbed. During this process just check if there is any temperature change on the LCD. If there is a change it means your thermistors are working. If there is no change at all, your thermistor is defective.

IPA Test = uneven heating

To see whether the surface is heating properly or at all, we suggest wiping down the heat bed surface with Isopropyl alcohol (IPA) cold and then preheating. The alcohol will evaporate when heated, exposing areas that are not heating at all. 

Loss of power = slow preheat process

Remove the printed cover at the back left of the heated bed and check following.

  1. Damaged Heated bed cables at any spot
  2. PSU cables properly attached to the miniRAMBO board and not damaged at any spot 

* Usually cables can be damaged around the Zip-ties. As this is the most stressful part of the cables*

**Please try the following if you have access to a multimeter to get some data to see if the heatbed components are out of spec or potentially problematic.**

If you are unfamiliar with how to use a multimeter, here is a good tutorial you can look over.

Measuring resistance:

  • The resistance of the heated bed thermistor should be approximately 100K at room temperature (same goes for the thermistor on the hot end if you are curious!)

  • The resistance of the heated bed should be 1 ohm (don't worry if the resistance oscillates around 1 ohm)

Measuring voltages:

  • The voltage coming to the heated bed should be ~12V
  • The voltage coming from the PSU to the Rambo Mini should be ~12V too.

If the issue persists after trying all the above, contact our support team at info@prusa3d.com. Be sure to include the fact that you've tried the above steps and any measurements you may have obtained.

How did we do?