Help required, Bug in my very first library

one thing i noticed just now is changing vRef between 3.3v and 5v does not affect the results at all.

Maybe this is the error

mickymik:
one thing i noticed just now is changing vRef between 3.3v and 5v does not affect the results at all.

If the reference voltage of the ADC is the same voltage supplied to the sensor arrangement (voltage divider) then the voltage gets cancelled out. (crap explanation but I'm tired)
If you take the following two lines (which I assume are correct):

	Vin = reading*_vRef/_RESO;
	float r = (Vin / (_vRef - Vin) * rRef);

You should find that you can mathematically simplify them until the voltages disappear. The equivalent code is:

float r = (float(reading) * rRef) / (_RESO - reading);

mickymik:
Do you have any ideas for possible solutions?
Is it feasible to add a second lookup table for ADC values? (i.e. would such a table work across all ESP32's, or is an individual solution needed for each device)?

You could read this thread and its links for some background.
I guess you could correct for the ESPs non-linearity before you pass the values into your getTemp(), but it's gonna be a hassle.