HELP..Temp is wrong

Great machine printed for 2 days whitout problems .The extruderhead pluged up and i cleaned it out. accedently broke 100K thermister
i replasted it whit a new working 100K Thermister but my board Melzi show 121 c but the head keep on heating up.. mesured the thermistor when hotend running hot . thermistor id dropping ok Damm Hwats wrong ..Hwat more can i Test Please Help and soory for my bad English ...Im Danish

Edited 1 time(s). Last edit at 02/24/2013 04:18PM by guf.

Can i swhits the pins somhow to get termister to Work on another pin.and WHO kan do the script.......

If the board is reporting changes in temperatures, then the controller pin and A/D converter is working and you will not need to switch pins.

Is the new 100K thermistor exactly the same as the old one? If not an exact replacement, you could need a different thermistor table/configuration to get accurate temperatures.

You could test the thermistor by checking its resistance against the expected resistance at different temperatures. If you can measure the temperatures accurately with a thermocouple, you could make your own thermistor table.

Check that the new thermistor isn't shorting to itself or the hotend.