Hot end heating past setpoint

[iras]

Hi, I'm working on a Geeetech i3 Pro that I bought from someone who couldn't get it working. I have most of the problems fixed, but still have a problem with the hotend.

It heats up, but then goes higher than the set temperature before settling down. For example, If I set the temperature to 180C, it goes over 205C before it stops heating. I've noticed that both the heating element and the thermistor are very loose in the metal block. That is probably the reason for this inaccuracy.

How should the heater and thermistor be secured into the metal block? This is a MK8 hotend.

Thanks.

[Mark]

tighten the set screws and use a cable tie or something to tie them up.

[iras]

I looked and expected to find a set screw, but didn't. I tried using some bare wire to take up the space between the heater and the block (to force the heater against the bored hole). Ditto for the thermistor. Didn't make a difference. When looking at the R-H temperature plot, the hotend initially overshoots by at least 20 degrees C (the heater power shuts off as soon as the thermistor says it reaches temperature), but the temp keeps rising. Once it drops down a few degrees below the setpoint, then it stays about +/- 5 degrees within the set point. Looks like at that point the Marlin firmware starts using PWM to control the heat more accurately. But I still don't know why it overshoots so much.

[Mark]

it's normal I think, my printer will also overshoots about 15 degrees sometimes, as long as it works all right then it won't be a problem.