The printer won't turn on or switches itself off

Symptom

Pressing the switch does nothing: no display, no fans. Or it starts and then shuts off, gets stuck in a boot loop, or turns off as soon as it starts heating.

Likely causes, from most to least likely

1. No power reaching it: socket, mains cable or switch.
2. Power supply cables loose or not tightened properly on the board.
3. A blown fuse on the board or in the power supply.
4. A damaged cable causing a short, for example with the insulation broken by an overtightened zip tie.
5. On supplies with a manual voltage selector, the selector doesn't match the mains; it may shut off when it starts heating.
6. The power supply has failed: its indicator light doesn't come on.

Checks to tell which one it is

• Test the socket with another appliance and check that the mains cable is fully plugged into the printer.
• Without opening anything, see whether the power supply has a visible indicator light and whether it comes on with the printer plugged in and switched on.
• If it starts and reboots in a loop, turn it off with the power supply switch (not with the display's reset button) and turn it on again.
• If it shuts off right when it starts heating, check the power supply's voltage selector, if it has one.
• With the printer unplugged, look for stripped, burnt or pinched cables, especially those of the power supply and the board.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Rule out the socket, cable and switch

   Try another socket, check that the mains cable is properly connected and that the switch is in the on position.

   Check: The display or fans come on.

   If that does not fix it: Restart from the power supply or check the connections.

2. If it boot-loops, switch it off at the power supply

   Switch it off with the power supply switch, wait a few seconds and switch it on again. Don't use the display's reset button for this.

   Check: It starts normally.

   If that does not fix it: Check the board connections.

3. Check connections and cables, unplugged

   Unplug the printer before opening anything. Check that the power supply cables are secure on the board, that connectors are seated and that no cable is stripped or crushed.

   Check: Everything is secure and undamaged, and the printer starts.

   If that does not fix it: Check the fuses.

4. Check the fuses

   If your printer has fuses (on the board or next to the power supply inlet), check with it unplugged whether any has a broken wire inside. Replace it only with one of the same type and rating; take the blown one to the shop to get it right. If it blows again, there's a short: don't keep trying.

   Check: With the new fuse, the printer turns on and works.

   If that does not fix it: Check the voltage selector or the power supply.

5. Check the voltage selector

   If your power supply has a manual voltage selector, unplug the printer and set it to your mains voltage.

   Check: It no longer shuts off when heating.

   If that does not fix it: Suspect the power supply.

6. If the power supply shows no sign of life

   If the power supply light doesn't come on, it may have failed. Don't open it: it contains dangerous components. Contact your manufacturer's support to have it checked or replaced.

   Check: With the supply checked or replaced, the printer turns on.

   If that does not fix it: Contact your manufacturer's support.

Prevention

• Don't overtighten zip ties on cables: they can damage the insulation and cause a short.
• Now and then, with the printer unplugged, check that the power cables are still secure.
• Keep spare fuses of the exact type your printer uses.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Printer does not turn on or keeps turning off · Prusa Research
• Blown Fuse (MK3/MK3S/MK3S+) · Prusa Research