Need help trouble shooting

Have no idea to trouble shoot this problem. My printer was was fine, then it hit my binder clip and made a spark. I turn it off then waited until complete rest with temp and nozzle cool down. Show my extrude over heated even tho I can touch it and it’s cold. I replug all my wires. I am at a lost now. I also have the skr mini 3 and have a pi connected if that helps


First of all, the hot end should be electrically isolated. It should never have caused a spark in the first place, so that’s something that needs attention.

Most likely related to the above, the “high” nozzle temperature is really just the thermistor giving a false reading which would be constant with it being shorted to the heater block. Ideally, there should be some high-temperature insulation on the thermistor leads during the last few cm where it enters the heater block. I’m guessing that insulation either isn’t there or has gradually worked it’s way out.

Now, there are several models of thermistor and I don’t know which one the Ender-3 uses so I’ll make some assumptions. Unplug the thermistor and measure the resistance across the terminals with the heater block at room temperature. Ideally, it should read around 10,000 ohms at 25C. I see that your heater bed shows the room is at 17C so you won’t actually read 10,000 ohms, but it should not be 0, nor should it be infinity. Note that some thermistors have a room temperature resistance of 100,000 ohms so the 10,000 ohms I’m quoting is one of the assumptions I’m making. Check your Ender 3 manual for what the correct value should be.

Also, be aware that thermistors come in two flavours: Negative, and Positive temperature coefficients. If it’s a Negative temperature coefficient, the resistance will go DOWN as the temperature rises. If it’s a Positive temperature coefficient, the temperature will go UP as the temperature rises, so, given that your room appears colder than 25C, if the Thermistor is the 10K Negative coefficient variety, at a room temperature of 17C, as shown on your display, you might reasonably expect to see a reading of 20K. I only point this out so you don’t think something’s wrong if that’s what you’re seeing.

So, if you’ve tested your thermistor and it seems OK, the next thing to check is the resistance between the nozzle and each of the thermistor wires. They should BOTH be infinity. If one of them shows 0 then it’s shorted to the heater block and you’ll need to find a way to insulate the lead so it doesn’t happen again.

This brings me around to my bigger fear. If one of the thermistor wires got shorted to ground, did this damage the controller board? First, check that the thermistor is behaving normally. If it is, the the circuitry that reads the thermistor may have been damaged.

The thermistor is the easiest and cheapest thing to test and replace, so start there.


From my understanding we have determine the nozzle temp issue but regarding the X Y it would change it value it a ? to a negative number. Is there relationship to the thermistor and the heater block, is it one problem or three problems?

It’s funny. I didn’t even notice the X, Y, Z values. I was too focused on the temperature discrepancy.

My printer is running so I can’t verify this, but I’m 99% sure the “?” marks simply indicate that the controller doesn’t know where the print head is, which is typical for a machine that has been restarted. Home the printer.

As for why it shows -? and -??, that I’m not sure of. It could simply mean that the X, Y and Z values it shows in memory were randomly initialised to something positively or negatively out of range, but I’m just taking an educated guess. Do an Auto Home and see if it goes away.

look like you are correct, today I learn