I'm trying to verify the correct hotend heater for a Reprap x400 Pro V3. I know a 12 V 40 W doesn't work. A working heater measures 4.4 Ω, so I'm guessing it is a 12 V 30 W heater.
When I tried replacing a non-functioning hotend heater on a German Reprap X400 V3 with a new 12V 40W heater that heater also wouldn't heat. My guess is the circuitry shut off due to overcurrent. The thermistor temperature didn't change from room temperature, and the heater was not hot to the touch. Afterward, I plugged in the heater measuring 4.4 Ω and it worked.
The 100k sensors worked properly. A functioning heater resistance measured 4.4 Ω. The non-functioning heater measured 3.6 Ω. The new 12 V 40 W heater measured 2.6 Ω. Apparently, this model Reprap won't apply power to the heater if the resistance is wrong. I'm assuming this model needs a 12 V 30 W heater, but am trying to confirm this since I can't find a parts bill of material for this model. Used the following equation to estimate heater resistance (voltage^2)/power = resistance. This gives 4.8 Ω for 12 V 30 W and 3.6 Ω for 12 V 40 W.