Keeping temperature constant

I have had mulitiple successful prints, actually almost all of them however recently when I try to print objects longer than two hours I get the M99 code shows up which I think I must have a bad connection somewhere but I just soldered all the wires together on my new thermistor. My rate of temp. seems to fluctuate a little too much. This picture below is what my temperature looks like when printing PET at 232C. It will look like this for a while and then a small spike and then dip in the curve followed by the M99 code and I have to restart my printer. This only happened twice within the last week, should I try to re-solder the connection? This problem doesn't happen often but I want to be able to fully trust my printer and be able to push run and then leave for an hour or so and no have to watch it.

-Bcamaro1

 

Tune your PID values using autotune. http://reprap.org/wiki/PID_Tuning

A dip is a sign of a loose connections. Make sure all your connectors are snug and all the pins are fully seated.

 

Thanks I will try this later on today and hopefully fix the problem.