Workhorse - AST285 - Extruder Won't Heat

I’ve been using the AST285 1.2mm tool head for a few weeks and I love it! Unfortunately I ran into a bit of a snag this morning.

Octoprint gave a thermal runaway error about 15% into a print, the third of the morning. Checking the printer physically revealed no apparent issue with flow/obstructions. I reset and tried again but now I’m getting a heating failed message. I’ve checked the wiring harness and don’t see any signs of singed insulation or melted contacts. I believe I’ve narrowed it down to either a bad thermistor or heater cartridge. Any advice or other information I could share to help diagnose?

Just look at the temp reading on the screen.

If it’s reading 0 temp when you first turn it on, thermistor’s no good or not connected.

If its temperature reading generally matches the bed temp when you first turn it on, thermistor is probably fine. If you then set a temperature for the hot end, and the temperature doesn’t start to raise after 5-10 seconds, your heater is no good or not connected.

Intermittent wire connection on either can cause the issue to appear any time during a print, and is harder to diagnose if you’re not watching the temp graph as it happens or are logging it.

1 Like

Appreciate the clear and concise tips. I used a soldering iron to confirm the thermistor is indeed working. It looks like the issue lies with the connection or the heater cartridge. My multimeter shows 24v coming from the mainboard when a temperature is set via the console. With the printer off and disconnected from power, I get continuity between the mainboard hot-end positive terminal and the output terminal in the wiring harness. The mainboard fuses also check out OK.

The negative heater cartridge wire in the internal wiring harness gave up the ghost. I spliced in a new wire and am back up an running.

Something worth noting from a source of a expert opinion there are plugs in the motherboard but please try and save it as a last resort keep in mind I am not a computer nerd in general & if you are a nerd or not its normal