[mikemc1]

front window demister only working on setting 4 . informed that this could be a faulty resistor if so is this an expensive fix or can it be done without going to a garage

[Leeky]

You could easily get one from the scrap yard if you feel like removing one.

What year, make and model is your car?

[mikemc1]

opel vectra 03, where is resistor located??

[gasser]

The resistor is mounted behind the glove box.Remove the 3 screws hoding the box, gently pull itforward and disconnect the light unit . The resistor is mounted above the rear of the glove box, is whit in colour and can be unclipped from its mounting.You can get a new resistor from Vaxhall but it will cost you about £40. the cheaper option is to cut away the thermal fuse,, get a replacement from Maplins (62p) and fit it with 2 screw connectors.
The problem with the resistor probably lies with the heater motor, Debris builds up in the drain tubes in the wiper compartment building up and blocking the exits, water can then get into the motor and seizing it. Check that the exits are not blocked by lifting the covering underneath the bonnet on the nearside under the wipers. This often leads to water leaks in to the passenger footwell also.