Preheat error (Heatbed) | Prusa Knowledge Base

Preheat error can happen with either with your Nozzle or Heated bed. So 1st make sure with which of these you have the problem.

"Heatbed preheat error" (Heatbed)

Things to check:

Make sure that your Heated bed thermistor is properly seated under the Golden Kapton tape (photo below)
Remove the cable cover from the back of the heated bed and inspect the leads to ensure they are still intact and soldered securely to the pads
For MK2/MK25: Make sure the heatbed connector is fully seated into the socket on the RamboMini - You should routinely check this in general!
If you've checked all the above and everything is in order. Please flash to the latest firmware.
Would the issue still persist, then there is for sure something wrong with your heater or thermistor. In order to find out which one of these is malfunctioning. Do the simple test described below.

How to find out if your Heater or Thermistor is defective for your Nozzle/ Heatbed?

It is not very common, but there is a chance that extensive printing damaged your heater or thermistor.

The easiest solution is to take a hairdryer and blow hot air at the Hotend or Heatbed. During this process just check if there is any temperature change on the LCD. If there is a change, it means that your thermistor is working, which means that the heater is damaged. If there is no change at all, your thermistor is defective.

Checking voltages and resistance

Using a multimeter would be the most efficient and accurate way of determining if the components are good or not. It is quite straight forward. See Multimeter usage for how and what to measure.

6 comments

Tom S

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almost 2 years ago

[solution hack] I had this problem in the past, and a new heatbed solved it... till recently, when I got the same error.I usually get the error when the printed element fell, and the printer started printing in thin air.
The first time, doing a flash to the newest software solved the issue for some prints, but then a thin element fell, it started printing in the air, and I had the usual "Heatbed preheat error again".
However, what solved it for me was starting the print - seeing that the heatbed wasn't warming up - and manually "kickstarting" the heatbed with a hairdryer. After that, I heated it up this way a few degrees, it did the rest itself and is now keeping a steady temperature.
As this has given me many grey hairs in the past, I wanted to share this solution here asap :) hope it can help someone.

Real 3D Prints

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over 2 years ago

I usually print PLA at a bed temp of 60, with many prints. I got this error the next day after printing two small parts with PETG at a bed temp of 83 for the first time in a year. I believe the extremely slight expansion and contraction of the screws and bed with this higher temp where it attaches left a less than perfect connection from the wires to the bed. I noticed that one of my heater wires, where it attaches to the bed, although firmly attached through the washer to the nut, was able to rotate, along with the nut. When I removed both of these screws and retightened them fully, the error went away and I could print again. There must be some sort of very exact measurement of voltage and if it is even slightly off the printer gives this error and wont heat the bed. In my case the connection was a little less than perfect with the wire connection, and printing with PETG made it go enough over a threshold to become a problem.

binel

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over 4 years ago

I believe that the issue arises when printing thin walls and despite saying "bed preheat error" it is not related to the termistor or to the bed. I observed it several times with tiny parts being printed. @Support I can provide a .3mf file so that you can reproduce the issue.

Giuliano - Official Prusa CS

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over 4 years ago

Hello. The support can have a look at your test file. If you wish to contact them, please write an email at [email protected].

jf2112pm

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over 4 years ago

I have a new MK3S and have done 3 small prints.15% into my fourth, the heatbed error shows up. numbers jump all over the place all the way to a190, 60 109 79 etcI have checked everything and it starts again and then same error pops up.I will try the hair dryer suggestion and see what results I getany other suggestions?

Official Prusa CS

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over 4 years ago

Hi, it sounds like your heatbed thermistor is damaged and doesn't report correct readings. Please contact our support to double-check it :)

fabio.f3

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almost 5 years ago

I own an MMU1 that was used for MMU2. I replaced the bed temperature sensor, check all connections and the problem persists. I do not know what else to do. Should I give up?

Official Prusa CS

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almost 5 years ago

Hi, please contact our support via livechat or email - we'll help you troubleshoot it.