<p>There could be a number of reasons for that behaviour:</p>

<p>Please check following items:</p>

<ol>
<li>part blower/fan cools down the nozzle - stop the fan</li>
<li>material is extruded at high speed and takes the heat</li>
<li>loose thermistor (when the move occurs as it moves a bit internally) </li>
<li>the power supply unit voltage varies - so temperature reading varies as well - measure voltage and see if there are significant drops</li>
<li>nozzle heater and thermistor cables can be loose as well (check screw terminals)</li>
<li>bed heater connection cables having not a good connection (check screw terminals)</li>
</ol>

CC BY-SA 4.0
2018-05-28T16:54:38.143Z
I am not using any fan to cool the nozzle.Fan which came with the extruder cools the metal part which holds the nozzle.This is my extruder [link](https://www.robotdigg.com/product/243/MK7-Dual-Stepextruder). Also the heating coil and Thermistor is fastened to the nozzle using grub screws. Thing that confuses me is that, sometimes the hot end temperature stays constant during print (+/- 0.5), but most times it varies drastically.
Athul
CC BY-SA 4.0
2018-05-28T16:54:43.317Z
Could be the issue of power supply. May be it can't supply enough current to motors and heating coil at the same time.But It's a 30A supply. I was thinking about checking it. Also the power supply s powered  by an Inverter.
Athul
CC BY-SA 4.0
2018-05-28T16:59:45.723Z
The point is that it could be broken wire (heater or thermistor) so it is not clear to see it. I'm case I replaced heater and got stable temperature
profesor79
CC BY-SA 4.0
2018-05-28T14:15:43.683Z
2018-05-28T14:28:50.767Z
2018-05-28T14:28:50.767Z
profesor79
<p>Dropping hot end temperatures can be caused by the filament cooler blowing too much cold air onto the nozzle, or a too high of a print speed so that the nozzle is cooled by the filament (in combination with a heating element that cannot heat that fast to compensate).</p>

<p>To rule out the PSU you could try measuring the voltage of the PSU before and after powering the heat bed, if it drops dramatically when the heat bed starts change the PSU.</p>

CC BY-SA 4.0
2018-05-28T14:17:50.343Z
nice timing Sir :)
profesor79
CC BY-SA 4.0
2018-05-28T14:19:34.717Z
Yours is more complete! But usually it is one of these.
0scar
CC BY-SA 4.0
2018-05-28T14:16:47.493Z
2018-05-29T18:13:24.960Z
2018-05-29T18:13:24.960Z
0scar
<p>My problem was like yours and after several test I found bad PID tunning in heated bed disturb hotend temperature process.</p>
<p>Before heated bed PID tunning:
<a href="https://i.sstatic.net/XH6RC.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/XH6RC.png" alt="enter image description here" /></a></p>
<p>When I fixed PID values for heated bed everything works like a charm :)</p>

CC BY-SA 4.0
2020-07-13T19:29:25.987Z
2020-07-13T19:29:25.987Z
Dani Díaz
<p>Can you also show a "power output" graph (or something like that, which show PWD duty cycle output to the hot end)?</p>

<p>Have you noted any relation between temperature raise and fall and the printing position?</p>

<p>Looking at graph I can only suggest the heating is suddenly stops and then the same sudden resumes.
It looks like you have a loose wire connection to the heater. When head is starting to move, it makes disturbance for the wiring, so heater occasionally stops to work.
There are usual two weak points: first it is where cable is connected to the board. Check is connector heated? Are any noises/sparks from there?
Another part: it is just at the point where wires going into the hot end. If wires are not secured to the printing head, then during printing those place experiences a lot of bending, which makes it weaker over the time.</p>

CC BY-SA 4.0
2018-05-29T14:13:53.247Z
2018-05-29T14:13:53.247Z
AterLux
<p>Hello I have had the same issue, fluctuating thermistor temperature, all of them. Discarding the board, and accessories setup (loose the heater, thermistor and so on) the problem was on the PSU. When I have opened the PSU and touched gently all the parts  then closed again and connected it to the printer: temperature readings were stable egain, however just for a time.</p>
<p>Fluctuations of temperature due to heating have in general low frequencies due to the heat transport phenomena in material such as plastic and metals especially if the amount of metal material is of the order of 100 grams.</p>
<p>Changes over the time with supplied power of about 500 watt over 100 grams of metal and plastic flow of a fewer grams per minute, seldom, cant cause temporal fluctuations  in frequencies of the order of electrical fluctuations. It's possible but not in 3D printing case.</p>

CC BY-SA 4.0
2020-06-22T19:50:56.663Z
2020-06-23T10:33:25.117Z
2020-06-23T10:33:25.117Z
Tomas Mora
<p>If I set temperature say 220 °C, printer heats up to it and it only varies +/- 0.5 °C under non operating condition. But if I start a print, there's a shift of +/- 15 °C.</p>
<p>I've already auto tuned PID parameters and when I run <code>M503</code>, the printer shows the updated PID values.</p>
<p><a href="https://i.sstatic.net/w8SCE.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/w8SCE.png" alt="Octoprint temperature graph showing hotend temperature drops" /></a></p>
<p>What could be the reason?</p>
<p>Electronics details:</p>
<ul>
<li>Firmware used:  Marlin</li>
<li>Controller board: Printrboard rev D</li>
</ul>

CC BY-SA 4.0
2018-05-29T18:11:57.130Z
The bed target is `off`, please explain why the bed temperature increased? E.g. did you shut of the bed prior to making the screenshot?
0scar
CC BY-SA 4.0
2020-07-12T09:06:42.223Z
Hello Athul, I noticed your question has been up for a while now. Have any of the answers below been able to solve your question? If so, would you mind accepting the appropriate answer. If not, what is missing so that we may help you further? Also, if you have figured it out on your own, you can always answer and accept your own solution. Thank you!
0scar
CC BY-SA 4.0
2020-07-13T08:56:39.433Z
@0scar I have replaced the Heater block, cartridge and Thermistor. I don't know which one of these solved the issue, that's why I haven't updated it as an answer
Athul
CC BY-SA 4.0
2020-11-13T20:36:45.057Z
what program did you use to get this charting?
user25313
CC BY-SA 4.0
2020-11-14T08:03:46.887Z
@user25313 OctoPrint
0scar
<marlin><hotend>
Hot end temperature varies during print
Athul
# Hot end temperature varies during print

(Asked by: username_0 on 2018-05-28)

If I set temperature say 220 °C, printer heats up to it and it only varies +/- 0.5 °C under non operating condition. But if I start a print, there's a shift of +/- 15 °C.

I've already auto tuned PID parameters and when I run `M503`, the printer shows the updated PID values.

[![Octoprint temperature graph showing hotend temperature drops](https://i.sstatic.net/w8SCE.png)](https://i.sstatic.net/w8SCE.png)

What could be the reason?

Electronics details:

* Firmware used: Marlin
* Controller board: Printrboard rev D

**Tags:** marlin, hotend

> **Comments:**
> **username_1**: The bed target is `off`, please explain why the bed temperature increased? E.g. did you shut of the bed prior to making the screenshot?  
> **username_1**: Hello username_0, I noticed your question has been up for a while now. Have any of the answers below been able to solve your question? If so, would you mind accepting the appropriate answer. If not, what is missing so that we may help you further? Also, if you have figured it out on your own, you can always answer and accept your own solution. Thank you!  
> **username_0**: @username_1 I have replaced the Heater block, cartridge and Thermistor. I don't know which one of these solved the issue, that's why I haven't updated it as an answer  
> **username_2**: what program did you use to get this charting?  
> **username_1**: @username_2 OctoPrint  

---

## 5 answers

### Answer by username_3 on 2018-05-28. Score: 6

There could be a number of reasons for that behaviour:

Please check following items:

1. part blower/fan cools down the nozzle - stop the fan
2. material is extruded at high speed and takes the heat
3. loose thermistor (when the move occurs as it moves a bit internally)
4. the power supply unit voltage varies - so temperature reading varies as well - measure voltage and see if there are significant drops
5. nozzle heater and thermistor cables can be loose as well (check screw terminals)
6. bed heater connection cables having not a good connection (check screw terminals)

> **Comments:**
> **username_0**: I am not using any fan to cool the nozzle.Fan which came with the extruder cools the metal part which holds the nozzle.This is my extruder [link](https://www.robotdigg.com/product/243/MK7-Dual-Stepextruder). Also the heating coil and Thermistor is fastened to the nozzle using grub screws. Thing that confuses me is that, sometimes the hot end temperature stays constant during print (+/- 0.5), but most times it varies drastically.  
> **username_0**: Could be the issue of power supply. May be it can't supply enough current to motors and heating coil at the same time.But It's a 30A supply. I was thinking about checking it. Also the power supply s powered  by an Inverter.  
> **username_3**: The point is that it could be broken wire (heater or thermistor) so it is not clear to see it. I'm case I replaced heater and got stable temperature  

---

### Answer by username_1 on 2018-05-28. Score: 2

Dropping hot end temperatures can be caused by the filament cooler blowing too much cold air onto the nozzle, or a too high of a print speed so that the nozzle is cooled by the filament (in combination with a heating element that cannot heat that fast to compensate).

To rule out the PSU you could try measuring the voltage of the PSU before and after powering the heat bed, if it drops dramatically when the heat bed starts change the PSU.

> **Comments:**
> **username_3**: nice timing Sir :)  
> **username_1**: Yours is more complete! But usually it is one of these.  

---

### Answer by username_4 on 2020-07-13. Score: 1

My problem was like yours and after several test I found bad PID tunning in heated bed disturb hotend temperature process.

Before heated bed PID tunning:
[![enter image description here](https://i.sstatic.net/XH6RC.png)](https://i.sstatic.net/XH6RC.png)

When I fixed PID values for heated bed everything works like a charm :)


---

### Answer by username_5 on 2018-05-29. Score: 0

Can you also show a "power output" graph (or something like that, which show PWD duty cycle output to the hot end)?

Have you noted any relation between temperature raise and fall and the printing position?

Looking at graph I can only suggest the heating is suddenly stops and then the same sudden resumes.
It looks like you have a loose wire connection to the heater. When head is starting to move, it makes disturbance for the wiring, so heater occasionally stops to work.
There are usual two weak points: first it is where cable is connected to the board. Check is connector heated? Are any noises/sparks from there?
Another part: it is just at the point where wires going into the hot end. If wires are not secured to the printing head, then during printing those place experiences a lot of bending, which makes it weaker over the time.


---

### Answer by username_6 on 2020-06-22. Score: 0

Hello I have had the same issue, fluctuating thermistor temperature, all of them. Discarding the board, and accessories setup (loose the heater, thermistor and so on) the problem was on the PSU. When I have opened the PSU and touched gently all the parts then closed again and connected it to the printer: temperature readings were stable egain, however just for a time.

Fluctuations of temperature due to heating have in general low frequencies due to the heat transport phenomena in material such as plastic and metals especially if the amount of metal material is of the order of 100 grams.

Changes over the time with supplied power of about 500 watt over 100 grams of metal and plastic flow of a fewer grams per minute, seldom, cant cause temporal fluctuations in frequencies of the order of electrical fluctuations. It's possible but not in 3D printing case.


---

