Hot-end temperature wildly fluctuates

What is the problem?

Before a print is started the hot-end temperature is consistently at 200C as reported by Octoprint. However, once a print is started the temp drops to around 160C and not consistent. This creates very under extruded prints. I can't remember the last time I had a good print. This was definitely happening last summer and I gave up printing until picking it up again now.

Here is the temp graph:


What did you already try to solve it?

Research suggested carrying out an auto-tune and then updating the printer PID values. This isn't something I have ever done before. After the first auto-tune the values came back as:

P=36.14, I=1.76, D=185.83

I updated a gcode file with these values but it made no difference so I carried out a second auto-tune. This time the values came back as:

P=26.50, I=1.17, D=150.33

Again, it made no difference to the print. I guess to me it seems like it probably isn't a PID issue but perhaps something more mechanical/physical with the printer.

Have you tried running in safe mode?


Did running in safe mode solve the problem?


Systeminfo Bundle

browser.user_agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36
connectivity.connection_ok: true
connectivity.enabled: true true
connectivity.resolution_ok: true
env.hardware.cores: 4
env.hardware.freq: 1200
env.hardware.ram: 917016576
env.os.bits: 32 linux
env.os.platform: linux2
env.plugins.pi_support.model: Raspberry Pi 3 Model B Rev 1.2
env.plugins.pi_support.octopi_version: 0.17.0
env.plugins.pi_support.throttle_state: 0x50000
env.python.pip: 19.3.1
env.python.version: 2.7.16
env.python.virtualenv: true
octoprint.safe_mode: false
octoprint.version: 1.6.1
systeminfo.generator: systemapi

Additional information about your setup

OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ... as much data as possible
Printer = Malyan M150
Octoprint version: 1.6.1

Any help is appreciated.


Does the part cooling fan on your printer point directly at the hotend? This definitely seems like something mechanical, but also it clearly doesn't have any thermal protection (unless this is just inside the boundary, which I doubt) from it not keeping temperature.

Well I guess it points very close to the hot end. Although I did take the fans off last year so I have just come to the realisation that maybe I have put either the cooling fan or the heatsink fan on the wrong way.

They are 'blowing air' out so they are taking the heat and disipating. Is this the wrong way?


The heatsink fan is usually on all the time, this shouldn't be an issue and if this is the case for you, then it is not that fan since it maintains temperature when the print is not in progress. The fan I am thinking of is the part cooling one, usually a blower-type fan that is pointed just below the nozzle to cool the print. If you heat the printer, then enable this fan (can be done in the control tab) then watch the temperature, we will be able to know if it is cooling the hotend too much.

I have tested enabling the fan via Octopi and whilst the temperature does vary slightly it isn't anything like what happens when I start printing. The arrow is when I started the fan:


So I guess this rules out an issue with the fan then :frowning:

Power supply?
You could try to compare the graph at slower print speed (less draft from the motors) and/or finer layers (less filament to melt per time). Are there any additional consumers like led strips?

When the part cooling fan blows too aggressive onto the heater block, I recommend a silicone sock for the hotend.

No additional consumables.

Good shout, I will do a test print at a slower speed and smaller layers and see what happens.