Hot end and thermistor not working

I am new to 3d printing. I am using the mega 2560 and rampd 1.4 board. I uploaded the marlin firmware and I am able to move all the stepper motors with the lcd encoder but my thermistor temp reads 345c and does not change if i try to warm the thermistor. Also the hot end does not heat at all. Could the thermistor be bad or is there a setting in marlin i missed? I selected the board and thermistor i am using. I even tried to select other thermistors in marlin.I currently only have the steppers and drivers connected as well as the hot end to d10 and the thermistor to t0.No endstops are not connected

Basic 100K thermister chart below

[www.bapihvac.com]

following thermister chart would have to be shorted 0 Ohms to be 345C, tested on my 3d Printer came up with 358C when thermister was shorted

Edited 1 time(s). Last edit at 02/18/2018 11:31AM by Roberts_Clif.

Its either a shorted thermistor of a bad mega or bad motherboard setting in firmware.

Just pull the thermistor cable off of the controller board, the temp should change to low temperature..

If it does your have a short somewhere in you thermistor or cable... (most probably at the heater block)

If it doesn't change check your motherboard setting is set correctly as a ramps and check your ramps and mega boards for solder blobs

My guess is dodgy wiring at the thermistor, I've had my thermistor do something similar after I fiddled with the hotend once. The wires aren't hard to break or short, so it's very possible this has happened. I recommend replacing the thermistor, it'll cost you cents but give you some peace of mind. Plus it isn't all that hard.

I just checked and it is shorted. Ill report back when i get a new one

One thing to check since it is a short, it could just be the insulation has been pulled down the leads and exposed them for a short, you may be able to fix this just by pushing the insulation back up the legs if this is the case.