Tevo Flash temp problem

So I got a TEVO Flash with which I printed about a week, then some filament started oozing from the hot end. I took it apart to clean it and I accidentally broke the thermistor, it was stuck in the hot end with hardened filament :(
I bought 3 new NTC 100k thermistors that show 164C at room temperature (I measured it with a multimeter and it displays about 100k). I tried a PID autotune but now it only goes from 164C to 200C. I am pretty sure the thermistors are ok, I can't figure out what am I doing wrong.
How is it possible to lower the room temp that is read by the thermistor? Do I have to change some settings in the firmware ? Maybe manually set it to another value in the firmware ?
Sorry, I am new to 3d printing and I don't know how exactly to troubleshoot this.

Thanks in advance.