E3 extruder not heating

OK, either
1) the heater core in the extruder is bad
or
2) the wiring TO the heater core is bad
or
3) the thermistor is failing
or
4) the RAMPS board is failing on the extruder heater output.

You can rule out 3 by seeing if it is actually feeling heat from the extruder when you tell it to heat or does it stay at room temp?
If it does not actually heat at all then 1, 2, or 4 are your culprits

If you can use the quick disconnects to disconnect the heater core from the hotend and put a multimeter across them and then tell the heater to heat the hotend. Do you have roughly 12vdc output to the heater core? If yes then the heater is bad and that is a cheap fix. If the answer is NO then you need to track the wiring back to the RAMPS board under the printer and make sure that there is no loose connectors or broken wires and that they are still solidly connected to the RAMPS board.

 

The heater core and the thermistor are very cheap.

https://www.partsbuilt.com/r1-heater-cartridge-robo-3d/

https://www.partsbuilt.com/r1-thermistor-robo-3d/

Replacing them is easy. Each have a set screw (use an M2 or M1.5 allen wrench) to loosen, slide them out and the use the disconnect to remove them from the wiring harness. Plug the new one in and replace it then snug up the set screw (not too tight) and you are done
'

 

Process is the same for most FDM printers:

 

The E3D is almost identical in terms of the heater core and thermistor replacement as are almost all FDM hotends. Only difference is exactly how they mount, but it is fairly obvious. All have a heater core and a thermistor as well as set screws to hold them in place.

Here is a video more specific to E3D:



You can find detailed instructions on E3D website as well.