Fan is enabled while heating?


Ich have a lot other issues which I don’t understand why this happen…

First Issue:
Suddenly, my K8400 cannot reach the needed nozzle temperature anymore.
I changed the Heater-Cardrigde and the Temperatur Sensor with a new one.
When I try to Load Filament, it tries to heat up to 220°C. But it does never reach that temperature anymore. I take a closer look and recognised, that the FAN is blowing and cools down the Heaterblock. When I manually switch of the FAN, it works, the temperature is reaching the triggerpoint and can carry on the process to load filament.

So. what is the quitessence? While heating the Nozzle, it is not necessary to cool it down with a FAN, do you agree with that?

My Solution for the “Load Filament Process” is: Changing the Code in ULTRALCD.CPP, switching the FAN off.

Second Issue…
Also when I start a print, the FAN is always on while heating. I swiched it off in the customizable Start-Sequence. With G-Code M107.

That works so far. But I wonder, was it ment to be?

Third Issue:
Again, related to FAN speed and Heating… While printing, the FAN begins to blow after finish printing the second layer (set in config). Then th temperature falls from 205°C to 180°C and cannot rise again. I do not understand why the Heater-Cardridge is not able to heat it up, even whe the FAN is cooling the Filament. Can you help me?

I already did an autocalibration of PID with M103 as described in another tread.
But its still not working.

I also played around with the configuration of the Filament setting, Section “Cooling”… Even when I set “Max Coolingspeed” to 1%, the FAN does not go lower than 60%. (As I see in the ManualControl Tab) Why is this so?

Uhhh so Sorry, so many question in one post… I hope, you can help me whith this temperature issues…

Thank you in advance

Hi maexchen,

not a problem at all.

For the temperature control please check out several other topics about temperature control within this forum, e.g.

This will explain, why a change of the temperature sensor will not automatically improve the situation, it may degrade it too.

So for the fan switched on it is clear that the heater has to provide more power with the fan switched on. There is a non-linear dependency between fan speed and heater power demand: it rises significantly when the fan is a low speed and increases slightly after reaching a speed level of approx. 30%. If the fan is cooling so effectively that the power control is at maximum level, then the temperature will drop until a thermal equilibrium is reached.

The standard K8400 firmware is not able to control the additional power demand by the fan in short time, so every change of the fan speed will generate a large deviation of the nozzle temperature for a short time. (some seconds).

Therefore I recommend to maintain the fan on a constant speed during the printing. This must not be 100% (due to power limit issues), but shall be sufficient to cool the PEEK isolator to reduce the risk of filament clogging. Within the reply of the temperature request (gcode M105) you can see the heater power level after the ‘@’ sign for each heater. Maximum level is 127.

You may improve the temperature behavior by tuning the PID parameters (correct gcode: M303), But after autotuning you have to get these parameters manually from the serial output, afterwards you have to install the new parameters manually (gcode: M304). However, I thing that I have found an error in the PID routine, therefore I modified it for better control and I don’t expect a better situation by default. PID parameter tuning is highly sophisticated.

I hope you will help you.

From firmware point of view the fan speed can be set to any value between 0 and 255, you can change the settings through the LCD “temperature” menu. So your cooling speed issue is manly a slicer issue.

Environment is everything to these machines.
What is the temp of the room it is in?

Hello hoh61

Many thanks for this very clear and understandable explanation! :slight_smile:

I am currently trying to fix the fanspeed for the whole print, incl. Layer 1. I found out, that my heater is able to keep the desired temperature constanty when the fan is on 35% (M106 S89).

I already did the auto PID settings, its very different to the original PID settings after installing. (Default - Setting provided from Velleman)

With these modifies settings, and not changing the fanspeed while printing, the printout seems to be better, but still not best… I keep experimenting… :slight_smile:

Many thanks!

best regards
René [Maexchen] Erdenberger

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I had my ups and downs with the K8400 ( and still have some). So to make the live easier ( or shorten the learning curve) I summarised my findings here: You are invited to share and improve.

Hello maexchen!

In my opinion this is really one of the biggest fails in “construction” of the Vertex printhead. 2 fans that should be driven independently are wired parallel with the same wires, the fans are blowing directly in direction of the heater cartridges and the mini front fan limites the y-axis to 180mm. As far as I can see there are no changes made for the current K8400.

The cleanest way to solve this problems: 2 separate wires for the radial fan on top, connected to the board instead of the almost useless bottom fan for the stepper cooling ( at least in standard setup without housing ) The fan for cooling the steppers could be directly wired to one of the pin pairs near the input for supply voltage ( eventually by using a separate controller for temperature).

Then you are able to change firmware settings for this fan from stepper cooling to hotend cooling and from now on the radial fan begins to blow with a programmable speed if one of the hotends reach 50° Celsius while the small front fan is controlled by g-code for filament cooling.

To fix the big problem with the fans (especially the radial one) are cooling down the heater cartridges you should place a aluminium sheet between the peek isolator guides and the heater cartridges with a little distance to each other. This sheet fits perfectly if you drill two holes with a little more than the diameter of the threaded part of the nozzles (for screwing into the peek isolator guides) and fix it with the two nozzles. It should cover the heater cartriges completely from top side. I used a 1.5mm aluminium sheet but 1mm should do the same. This has two advantages: First is that it blocks heat from the cartridges from rising upwards to the isolator guides and second it prevents the cartriges from beeing cooled down by the fan(s).

Additionally I printed a new fan guide for the radial fan and widened the opening in the aluminuum plate where the hotends are mounted as far as possible to guide some of the airflow down to the aluminium “heatbreak” Also I closed the holes on bottom of the plastic housing for the guide bearings by using another sheet of aluminium and machined a slot on top side of the bottom plastic part which lets the air aut directly above the heatbreak.

Works perfectly for me for over a year now. No problem to reach higher temperatures without changing the heater cartridge(s) A lot of work but it payes off in my opinion.

By the way: by another fan design my travel of the y- axis is 200mm instead of 180 but the cooling for PLA is a little too weak. I will try out a diapragm pump next time.
There should be a few older posts including pictures and a drawing for the aluminium sheet.

Kind regards


this is my mod, but still in progress

New XY-block (white one) with much more space for wind inside + small air nozzle (yellow part)

New fan duct (orange one) with 4020 turbine

about heartbreaks cooling: I want to use micro fan connected to heater in parallel with diode and capacitor 10uF to change PWM into DC, so fan should operate when heater is on.

You can see: heat blocks are wrapped using capton tape so they are more air-resistant.