There is a message on my Ender 6 that is telling my that my heating failed. This happened last night in the middle of a print. I have cycled the power like the screen says but the nozzle does not heat up. The print bed heats up just fine. The nozzle stopped heating and just randomly started cooling, leading to a load of filament unable to go through the feeder. The printer has been just fine for the past year in a closet. I have changed rooms and tested again to no avail, so I believe it is not an ambient issue. I would appreciate any advice or solutions.
If heating of the hot end fails, this is usually caused by the thermistor or the heating cartridge. You need to check the cables of these two or replace them altogether. It is advisable to keep spare heater cartridges and thermistors.
Once the thermistor doesn't register a temperature increase while the heater is on, a thermal runaway error should trigger the printer to stop to protect itself and you. That is, if the printer has this functionality enabled in the firmware. By removing the thermistor from the hotend and heating up the hotend you can test whether thermal runaway protection is enabled.
If the hotend drops in temperature, e.g. by a mispositioned cooling fan, the heater element should be commanded to heat up, if this doesn't happen, the protection should kick in as well.
There is a message on my Ender 6 that is telling my that my heating failed
This means that the thermal protection is enabled and did its job! You now need to sort out what caused the protection to kick in, a faulty thermistor or a faulty heater cartridge (or even worse, a faulty controller board e.g. burned connectors); cables could be broken or are not properly seated in the controller board connectors.