Filament will not retract beyond the head cooler

Vertex 3D Printer Vertex - Issues while printing
1

Hello,

The printing goes well, only when I retract the filament, it will not pass out of the cooler (beige plastic cylinder) i.e. it is blocked.
Reason is, the filament is enlarged (too wide, on about 5mm length), probably due to heat.

The coolers are new and the teflon tube inside looks ok to me (23mm length).
I print PLA @ 190°C, flow 78%, retraction 4mm speed 100mm/s
It went OK for many months and I don’t really spot a change that could be the reason. I regularly adjust/fine-tune/experiment the head (dual head).

Any idea ?

Tx !

2

It could be the thermistor : check it it’s well positioned and if possible the real temperature of the heater block.

3

Thank you.
I tried an infrared thermometer but that do not measure accurately such small surfaces, a thermocoupler thing is required I guess…
BR

4

[quote=“benoitmabille”]a thermocoupler thing is required I guess…[/quote]Indeed. And even with it you need a good thermal contact.