Temp not matching heatbed #12209 (MINI/MINI+)

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What happened?

The printer displays the message "Temp not matching - Measured temperature is not matching expected value. Check the thermistor is in contact with heatbed. In case of damage, replace it." when the measured temperature is different from the temperature expected for the heatbed.

This can happen if any thermistor failure on the heatbed causes the printer to read the temperature within a few degrees from the target temperature, but not the target temperature itself. The heater will keep trying to heat up while the target temperature is not reached. To prevent overheating the printer generates the error.

The error might indicate some issue with the wiring, either the heater or the thermistor cables are possibly damaged.

A visual inspection

Check the heatbed, where the thermistor and heater reside, and that no wires have broken off the sensor or heater themselves. Carefully try to move the cables by hand while the printer is turned off. If any of them have come detached your search is over and the part needs to be changed. It is not recommended to solder these wires, moreover, for the thermistor, it will change its resistance and thus readings. Spare parts can be found in our e-shop, or you can contact Support for assistance.

Try preheating the heatbed in LCD menu -> Control -> Temperature -> Heatbed to 90 ºC. After reaching the temperature, move the cables behind the heatbed by hand to see if the error will appear. In case the LCD main screen shows 0/0 in the heatbed temperature, check the cable connections to the Buddy board.

Loosen the one screw securing the cover (circled in the picture below), remove the top cable cover, and flip it open to reveal the board.

Check that all the connectors are secure in their sockets, according to the picture below. Focus on the thermistor and heater cables (yellow arrows). Though unlikely, rough shipping or handling could have shaken the heater or thermistor cables loose.

Checking the resistance

The table below describes the correct resistance for each part and what scale you should set your meter to. We have another more in-depth guide on Multimeter usage. All thermistors are rated to be 100 kΩ at 25 °C. To be realistic, with a varying temperature between 20 °C and 30 °C, you can expect a wider range of readings (~85-125 kΩ) than with the heater.

There can be micro-fractures in the cable, breaking the connections only at certain positions. Therefore, try to move the cable while measuring and see if the value changes drastically.

Where to measure

For every component, there are several options, our main focus will be on the connectors. The measurement appears on the multimeter LCD as soon as the measurement probes touch the component. To obtain the correct and relevant values, this is where you need to apply the probes:

• Thermistors: metal inserts in plastic connectors

• Heater cables: screws holding the cables in the connector

The hot end and heat bed have the same connector. Make sure you measure the correct one.

Parts replacement guide(s)

In case you find some parts are faulty, please order them using our e-shop, then follow the service guide(s):

How to replace a heatbed thermistor (MINI/MINI+)

How to replace a heatbed (MINI/MINI+)