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Hotend fan is not spinning

Last updated 4 years ago
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This issue can be preceded by the error Err: EXTR. FAN ERROR. Before we start checking your Hotend fan, power down and unplug your USB cable if it's connected. Open the electronics covering and examine the Mini RAMBo electronics wiring (MK2S, MK2.5, MK2.5S) or Einsy RAMBo electronics wiring (MK3/MK3S/MK3S+).

Make sure that the fan is:

  1. Plugged into the right connector.
  2. Plugged in with the proper connector orientation.
  3. Plugged in completely and making good electrical contact.

You can easily test the nozzle Hotend fan function from the LCD menu Preheat - PLA. From when the Hotend temperature reaches 50 °C, the fan should immediately spin up.

On MK2.5S/MK3S - From the LCD menu - Support - Extruder Info, you can find the RPM reading of the 3-wire fans that support this. The expected range should be from ~3500 - 4200 RPM on both fans, when run at full speed. Only the print fan speed can be adjusted by the user.

If the fan doesn't spin up, you can unplug it from the electronics board and test it with the 12V DC (MK2/S) or 5V DC (MK3) power source. If the fan spins up to an external power source, check all the electronics wiring in Mini RAMBo electronics wiring (MK2S, MK2.5, MK2.5S) or Einsy RAMBo electronics wiring (MK3/MK3S/MK3S+) and potentially a Blown Fuse (MK2S/MK2.5/MK2.5S). If the fan has a yellow sensor wire, it must be connected to ground (GND) for the fan to spin.

When the Hotend fan should actually spin

Hotend cooling fan cools down the top part of the Hotend (heatsink) from the heat which is transferred from the heater block. It always starts up when Hotend temperature reading reaches 50°C and spins for the whole duration of the print! If the fan is not functioning, you can expect the nozzle to jam after the first few layers due to heat creep.

Always make sure that the fan is pushing the air in through and around the heatsink and not out. The proper orientation of the hotend fan can be checked with the photo below.
Correct: Sticker facing inwardsNOT Correct: Sticker facing outwards
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