Hotend preheat error

What happened?

The printer is showing the message "Hotend preheat error: Check the print head heater and thermistor wiring for potential damage"

Error name: Hotend preheat error

Error code: #28202 (MK3.5S) #23202 (MK3.5)

This error is shown when the printer is unable to heat up the nozzle more than 2 ºC for 20 seconds. The printer starts a safety feature, which instantly kills the heating process and displays 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?

1. Make sure that the ambient temperature where the printer is stable, and above 10 ºC.
2. Make sure the thermistor and heater are properly plugged into the electronics board. You can double-check that by following the related step of the MK3.5/S assembly guide. 
3. Check if the fuses are not blown. 
4. Make sure that your hotend assembly is correct.

If the issue persists, the error likely stemmed from an issue with the hotend heater or hotend thermistor. To find out which one of these two is malfunctioning, perform the test described below.

Use a hairdryer to blow hot air towards the hotend. In the meantime, check if there is any temperature change on the LCD screen.

• If there is a positive temperature change it means that the hotend thermistor is working and detecting the temperature change. Most likely, the issue stems from the hotend heater. 
• If there is no change at all, most likely the hotend thermistor is causing the issue, or at least contributing to it.