Heating failed on Prusa i3

So this weird error started popping up...
Everytime I try to heat up the extruder to print something (and do this just via GCode), the measured temperature will rise fine up until 220 deg (when 230 °C is the target), and will then stop there, forcing the firmware to spit the "Heating failed" error.
I can't understand where this is coming from, not really. The error started appearing after separating the heater fan (for the heatsink) and the cooling fan (for the prints) so that the heatsink fan is always on, to prevent jamming.
I have tried retuning the PID controller, with no luck. The values I get are really close to the ones I had previously. Also, the extruder has always worked even with the fan on (even though it was gradually turned on mid print), so I don't think it can be an insulation issue...
The only thing I haven't done yet is change the section of the firmware where the watch temp is declared, but I don't think that will help in any way, as the temperature DOES NOT increase any further.
As far as my understanding of Marlin goes, I know that the PID controller kicks in by default when the temperature is about 10°C from the target (right?), so I'm guessing there's something wrong with it... Maybe autotuning didn't work?

Soooo... I've continued trying to figure it out... First of, I hadn't thought about EEPROM, so when I flashed the firmware with the new Kp, Ki, Kd values the printer was using those from memory. So I've put the right values in. The weird thing was, the extruder got to 220 °C, then fluctuated a bit around that temperature, but not enough time that it would trigger the failsafe, and then slowly and painfully got to 230°C. Then printing started. At the 5th layer, when the cooling fan went on from 80% to 100% the print stopped because of "Thermal runaway".
Strange thing is: it used to work. I can't imagine what it's making it go wrong, and heat badly. Any suggestions?

Check the power connections for the hotend heater. You may not be getting full voltage to it.

But why would the extruder work while PID testing and not otherwise? Anyway, I'll check in a few minutes and report back...

After testing, the cables are firmly connected, and the plug does in fact provide 12V as expected. What else could there be causing the PID not to kick in properly?

Edit: another round of testing. This time I have increased the printing temperature by 10°C. At the very moment the PID kicks in (around 230°C) the temperature stops increasing, and the Heating failed message pops up. Any insights? It seems to me the extruder is well capable of handling those temperatures, so it must be a software issue?

Edited 1 time(s). Last edit at 08/15/2016 09:27AM by Aschie4589.

I'll resuscitate my post because I'm still not getting anywhere...

The printer has now been working for some time (read: no more than 5-10 prints), and I had managed to solve the heating problem by just switching to bang-bang mode. Everything seemed fine (although temperature fluctuated quite a bit), but the last 3/4 prints all have had the same problem, thermal runaway, which made me switch back to PID controlled temperature... So... It seems constant in happening after 10/20% of the print is done, usually 45-90 minutes after starting. I don't have the printer connected to a PC, so i can't provide detailed graphs, but I see that the registered temperature, the one the LCD freezes over, is 222 out of 230 degrees.
I don't understand what it might be. It's too late for it to be connected to the fan turning on (it does that completely after 1.2mm), and it doesn't seem to be related to the physical conditions of the printer. I don't think it can be a heating problem, as the resistance works just fine. I don't know about the thermistor, so I can't exclude that completely, but that sensor has been performing quite well overtime, and the bowden assemby I'm mounting is fairly new.
Any ideas? Might it be related to firmware? Could it be in some way caused by read errors in the SD?

Once again, thanks for your help!

I have only been playing with my Hictop 3D printer for about 3 months, but have worked on electronics and machines for some time. I got the extruder temp fault during my first runs. I removed and checked the temp sensor- okay. After poking it back into the block I tightened the set screw finger-tight (just feel it touch the sensor "bead") then maybe another 1/8 ~ 1/4 turn. It appears that the sensor and or leads right at the bead might have gotten pinched as the heater block heated and expanded. The nozzle head does shake on some passes,so you might use a touch of white glue on the set screw if you are worried about it backing out. It's not as "permanent" as most thread-lock products. Hope this is helpful!

Might be usefull to explain how you changed the fan wiring. Also if this is happening after 45mins have you considered heat issues on the controller/driver board.

Found it! I've taken my time to do a bit of testing... It seems the problem was insufficient cooling on the electronics. Which means I'll upgrade to a MUCH bigger fan. Still in the process of testing though... Thanks again to all of you that helped me...

Update to pevious post: It could be the temp you are trying to run the nozzle at. My printer does not like nozzle temps below 175. Most likely something that can be changed in firmware, but I'll leave that alone for now
If any of you should find that the problem is with the temp sensor, DON"T overtighten the set screw! Tighten it to just touching. Don't tighten any further!

Edited 1 time(s). Last edit at 10/15/2016 07:58PM by davmart12.

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davmart12
If any of you should find that the problem is with the temp sensor, DON"T overtighten the set screw! Tighten it to just touching. Don't tighten any further!

What hotend uses a setscrew on the thermistor? A set screw on a glass package would be insanity.

I must say I'm now confused... and embarassed... since it still doesn't work

All right... here's the thing. I seem to have tried almost everything. I printed with and without cooling fans, with PID controlled heating and with bang bang controlled heating, I tried tuning the PID, changing the thermal runaway parameters (up to 10 degrees and 70 seconds). I have tried different models, with different kinds of shapes. I have tried cooling the controller, and that helped a bit. I shielded the hotend from strange airflows coming from the improvised RAMPS cooling solution. I have tried all I can think of. And I still manage to fail prints. This is getting very frustrating.

I know for a fact that the heater works (and by the way, I tried both tightening and replacing the set screws on my bowden extruder), since it successfully heats up. I know that the mechanics work and that the controller doesn't overheat. I know that the thermistors read correct values, and that they are reliable enough for me.

Every single print I've tried in the last days has failed. At right about 45-50 minutes. It almost seems like the error is timed. And yet it's not an SD card error (even if that would be quite weird) nor a fail in the model that is too difficult to print. I'm at loss. I looked around online and the only thing I could find was something about the fan wires possibly causing interference when too close to the hotend. But from the one graph I was able to get through Repetier, the temperature didn't float. It didn't change. It just slowly started to go down and in a couple minutes' time it triggered the error. Just like that, without any other esitation.

Any other insight would be much appreciated!

Have you considered that you might have broken cartridge heater?

If it's climbing to temp and then failing after a certain time it might just be expanding with the heat to a point that it fails.

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Out of the box thinking is easier when you never fitted in the box to begin with.

I guess what you suggest is I try buying a new hotend assembly? (Which is about the same price as the cartridge itself for me)
I'll give it a try then... I've been thinking myself that nothing can really be done...

Can you post photos of the hotend so that we can see the arrangement of the fans? And which firmware are you using? If the problem started when you changed the fans then there's a chance that the firmware simply isn't providing enough power to reach the specified temperature, perhaps because the fan is cooling the hotend.

A cartridge heater is really cheap depending where you are from in the world it shouldn't cost you more than a hotend.

---

Out of the box thinking is easier when you never fitted in the box to begin with.

Hi,
I too have a Hictop Prusa i3 with a heating failed problem. Only with me it seems to be the bed causing the problem. I got this at Christmas, and everywhere people are talking about 12v power supplies. Mine shipped with a 24v 15A PSU, but when I check the voltage at the bed terminals I'm only getting 23.5v - is this right? The heating failure occurs randomly at the beginning of a print, normally one or two layers in. I do have a 20A PSU, but I'm loathe to use it in case I blow the board. I have already replaced the Heater cartridge in the extruder, the thermistor in the block and even a new bed, but I still get the same problem. I need help as it took me a while to convince my wife that it was a neat bit of kit.
Cheers

Just a thought, would beefing up the wiring help? If I've got my maths right 24V 15A is the same as 12V 30A.

Sorry to be a pain, but now I've checked the heater connections and the voltage is all over the place, I guess that it varies as it tries to maintain the temp.

The only thing left for me to cahnge after the wires and PSU is the main board

The saga continues......... I've had the printer heated for the last 10 minutes at 240 at the head and 100 at the bed. It's ticking along nicely which leads me to believe that the PSU just can't cope with heating and motors. Am I way off the mark here? I know there are some real genius out there so please help an old guy trying to keep up with tech

I'm not quite clear on exactly what you're seeing. You said you thought the problem was with the bed and not the extruder - what was that based on? Are you looking at heating graphs in host software? If so, could you post screen-grabs of the graphs for us to see? If the graphs show spikes to lower temperatures as the printer moves that's typically an indicator of an intermittent connection increasing the resistance as the wire flexes. More gradual downward trends often correlate to part cooling fans turning on and overwhelming an uninsulated hot-end or an underpowered bed.

Dizzybear,

your PSU is 360W which ought to be enough compared with say the 240W ones provided with the Anet A8.

It's not clear whether the 23.5V you are getting is under load or not. It wouldn't hurt to adjust the PSU up to 24V. However if the heating problem only appears when the printer is printing and moving then it could be that you have a poor contact somewhere that is flexing and clearing as the printer moves. Start by re-checking all your 24V power connections from the PSU to the board and from the board to the bed and extruder. If there are screw connections in the run then terminate the cables with the correct size crimp-on connectors and tighten all connections. Some beds have two sets of connections 12V and 24V, make sure that you have connected the 24V ones.

If you can't get any improvement, and the PSU voltage is still varying under load, it could simply be a poor power supply.

Edited 2 time(s). Last edit at 01/09/2017 06:08PM by Supermec.

Quote
Dizybear
Just a thought, would beefing up the wiring help? If I've got my maths right 24V 15A is the same as 12V 30A.

If the wires from the power supply thru to the bed are not man enough for the amps , then yes you will get a voltage drop across them

Hi James,
I measured the voltage across the black & yellow pins as the bed was heating, so yes, it was under load. I have noticed prior to me changing a few bits that I could have the head heating without a problem, but if I heated the bed in isolation it would return the Failed heating message,

Dizybear - did you confirm the bed is set for 24V. If its set for 12V you will be drawing about 15amps. If the driver survives you will have maxed out your PSU.
Chances are the driver is limiting the current but the hot end can be doing the same.
Aschie - whats the latest on your issue? Yours seems to be a software issue - The error message "thermal runaway" is being triggered when the temperature is dropping. We need someone familiar with the software to jump in here. I am assuming this is the thermall runaway protection feature.
Seems like your hot end is only just capable of getting to target temp. When you put the cooling fan on its dropping the temperature and the hot end can't recover to target. The software logic compares the fact that the hot end is on max with the reported temperature and recognises its not increasing so flags the error on the assumption that the thermistor is not attached.
I have seen issues with the temperature tables being incorrect so it is worth having a look to see if the values are out of sequence. Also double check you have the correct table/resistor selected.

MCcarman,
Thanks for the info, I haven't checked the bed voltage setting - where will I find it? I'm at work ATM so won't be able to check for a few hours. I'm hoping to spend some time this afternoon fine tuning a hammer to hit it with

Cheers
Dizzybear

The bed voltage is usually printed on it. If its capable of being configured for 12v or 24v this is done by soldering the wires to the appropriate pads at the edge of the board. This is also marked on the bed. Just do a search for "3d heated bed 24v" and you should get a load of images.

To everyone that helpe with their expertise, a very heartfelt thank you. I have now finally sorted out the problem. Unfortunately I have to hang my head in shame as it turned out to be something even simpler than I first thought. I had broken the blower duct onto the extruder, so I printed off another one that I found on MYminifactory. I never noticed that the new one blew cold air staight onto the extruder, cooling quicker than it could warm up resulting in a heating failed message. So, armed with sellotape and cardboard I made up a vane to redirect the air onto the workpiece and TADAAAH! everything works as normal. I have since printed another duct that is the correct shape and it's still working fine 24 hours later. There should be a picture attached, not the best but I think you can see what I've done.

Once again, a big thank you to those helpful people who took the time to help, and the laugh's on me.

Cheers all

Dizzybear

Glad you got it sorted out, well done

Thanks for that Dizzybear I found I had similar issues.