I will try the thermistor thing and try and get some new nozzles.

Qidi have advised to replace the motor line which i thought was pointless???

Quote Originally Posted by Alibert View Post
Most likely a clogged nozzle. I never bother with cleaning nozzles, I just throw them away and use a new one as I buy them wholesale from Aliexpress at dirt cheap prices. No rocket science there, just a piece of machined brass or steel.

Another more difficult problem can be the thermistor which is used to measure and regulate the hot end temperature. I serviced a printer once which also had these weird problems. It turned out that the thermistor leads were making contact at certain movements of the extruder head. This results in a short which appears as the maximum temperature to the motherboard (300 C in this case). The motherboard then stops heating the hotend in order to cool of. However, as the hotend was the correct 230 C at that point, it cooled down and the plastic solidified in the nozzle. After tweaking things around, the short would disappear and the printer would work normally again, until the next times the leads shorted again, etc.

I finally found that one by monitoring the temperature in the control software, and jiggling the lead of the thermistor around. I could then see the temperature 'jumping up' to 300C at certain movements. Replaced the leads and problem solved.