The last few days I've had really horrible prints after months of my printer working well. Then things got worse, with emergency halts happening from time to time. It occurred to me to look at the temperature graph in Repetier, which looked like this: [goo.gl]. This only happened when the printer was actually doing a print: if I set the temperature and let it stand, it was completely stable. Replacing the thermistor didn't fix it. Replacing the thermistor wiring did. There is no obvious damage on a visual inspection (like a nick in the insulation), so I assume that the constant flexing of the wire caused it to partly break. Now the temperature looks like this: [goo.gl].

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See my blog at [moosteria.blogspot.com].

I will put this solution in my toolbox. Thank you for sharing your experience !

Yes, I had exactly the same thing a couple of weeks back. After I replaced the wire I spent some time trying to locate the fault in the original one and wasn't able to, which was a bit unsettling. It does seem that it's worth investing in good quality flexible wire for the runs to the print head, as well as trying to maximise the radius on the cable chain. I'm still not sure what the best way to go is on this, but I'm reminded of a post by DD about using some sort of ribbon cable. Right now I'm wondering which wire will be next to go, and hoping it isn't a stepper cable that could potentially take out the driver as well.