Extruder temp not matching #17210 (XL)

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What happened?

The Original Prusa XL continuously monitors the temperature of the tool head in use and its variation with respect to an expected reference. In case the printer recognizes a variation out of the acceptable range, it will display the following message: "Measured temperature is not matching expected value. Check if the thermistor is in contact with the heaterblock. In case of damage, replace it".

Error name: Hotend temp not matching 

Error code: #17210

In this case, the printer will stop the heating and display the message on the screen. The printer then waits for the user to inspect all parts and if needed fix the issue.

How to fix it?

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

A visual inspection

Before breaking out the multimeter you should check the Dwarf board, where the thermistor and heater reside, to ensure that no wires have broken off, or are disconnected. 

Place an empty Prusament cardboard box approximately to the front center part of the heated. Move the X-axis all the way to the front side of the printer, and move the extruder approximately to the center of the X-axis.

Open the dwarf-cover-door to access the Dwarf board.

Check that all the connectors are secure in their sockets, according to the picture below. Focus on the thermistor and heater cables. 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, as well as what scale you should set your meter to. The hotend thermistor is 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 (~80-125 kΩ).

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