MK4 heatbed error #13201: Diagnosis and solution (video link included)  

MK4 heatbed error #13201: Diagnosis and solution (video link included)

About a month ago, I built an MK4 from a kit and started printing with it. I've printed about 50 models so far, and the hardware has been a dream (but the firmware needs some work).

A few days ago, I started a print and then found the printer flashing error code #13201: Bed preheat error.

I reset the printer and then manually set the print bed temperature and was surprised that it didn't increase above room temperature. About 30 seconds later, the printer detected the problem and then returned the same error code.

All of this was surprising because nothing with my printer had changed. I had printed about six instances of a pretty simple model (a filament spool desiccant canister) and everything had gone swimmingly until it suddenly returned an error.

I unplugged the printer and started following the instructions in the Prusa page noted above. I unbolted a few parts, including the heatbed-cable-cover-top, and inspected the cables - no obvious problem.

I tried preheating the bed again... and it preheated just fine, all the way to 50 C. I also noticed that the heat LED near the terminals (ordinarily covered by the heatbed-cable-cover-top) was on.

I reassembled the heatbed parts and tried preheating the bed again... no heat. Also, the LED near the terminals was no longer on during a preheat command.

Long story short: The heatbed-cable-cover-top is the problem. Since this problem was repeatable, I recorded this video to demonstrate the problem. When it is installed - not even bolted in, just sitting on top of the terminals - the bed does not heat and the LED does not light. When it is removed, the LED turns on immediately and it starts heating.

This result is surprising, since the Prusa web page for this error message does not suggest anything about the cover as a possible culprit.

I presume that the heatbed-cable-cover-top is pressing down on some part of the terminals or LED when it is in position. Of course, I am neither forcing the cover down onto the terminals nor bolting it in with excessive pressure - as you can see in the video, the cover isn't even bolted in. I inspected the plastic cover and did not find any print defects that might cause a clearance issue when installed.