Thermistor MAXTEMP issue

Hey guys, first post here. So I'm building a Prusa i3 and I've nearly finished it although I have one last problem that has me stumped. I couldn't find a solution to my exact problem online so I thought I'd make a post here...
Basically what happens is: If I heat up the hot end and move the X-axis around, the thermistor jumps to around 358 degrees and I get the MAXTEMP error. The thermistor does indeed work because it reads room temperature accurately and matches the bed thermistor and can read temperatures like 200 degrees which leads me to believe it isn't a problem with the config or the Arduino/Ramps board. Only when the hot end is heated and I move around the extruder (or even give it a tap) it will jump up to 358.

I think it may have something to do with physical pressure on the thermistor because I initially had the same problem with the bed. The bed thermistor is sandwiched in a little groove between the bed and build plate. However when I first assembled it, the thermistor wasn't sitting correctly in the groove and when I leveled the build plate and brought it down it put pressure on the thermistor and made it read 358. Loosening the bed would bring the temperature back to normal (I fixed this by putting the thermistor in the groove properly lol but I have no idea how I could fix the hot end thermistor as it is clearly properly sitting in the hole cut out for it). Oh yeah I might add that it's a J-Head hot end.

So yeah if anyone else has had this problem or if I'm missing something obvious feel free to share your knowledge!

Thanks in advance and apologies for potentially being a potato. It's my first time building a RepRap. xD

How did you wired your thermistor? It sounds to me that one of the connections is loose. Check your solder points if you solder the thermistor ends or the connectors attached to the thermistor.

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ggherbaz
How did you wired your thermistor? It sounds to me that one of the connections is loose. Check your solder points if you solder the thermistor ends or the connectors attached to the thermistor.

I'm pretty sure it's all wired fine because I can move it around as much as I want at room temperature.

I had a very similar problem, I think there was a problem with the insulation on the thermistor wires and it was shorting out to the hot end body, but only did this when it was hot. So take out the thermistor, check the wires and very carefully put it back double checking you have plenty of insulation on the wires and do not over tighten the bolt (if there is one on yours) that holds it in place.

Dave