Hi, had problems lately with my heater- bad wiring etc- also had to change the heater resistor. Used a second hand one out of a '00 Punto. Heater fan working fine again but the resistor heats up a lot even after just a few minutes working. It gets about as hot as a light bulb. Is this normal or should I be worried? Thanks Vincent

I am no expert on these, but if the car has a PTC heater isn't the resisitor meant to get hot ?

You could be right.

Might it be worthwhile to try a Doblo heater resistor, or are they exactly the same?

I have been told by the parts supplier that their the same even though they look slightly different.

A resistor dissipates the current through it as heat, think about OHMS law, if the resistance is 10 ohms and 2 amps are flowing then 40 watts of heat will be generated.
I would be more worried if the resistor was cold as it would either be open or short circuit!

(the long calculation is R x I = V (above 20volts) V x I = P (in watts) which is 40 watts

Or for this calculation (the short way) P = V2/R