Got an issue with the heater I have replaced the unit under the dashboard and it still won't work it only works on number 4 switch 123 don't work any ideas at all 

 

Hi J.B.2.2, I had this problem on my astra when I first got it. It turned out to be the heat control sensor on the heater. I replaced it and all the controls on the heater now work. It was a fiddly job, as on the astra, the glove box had to be removed for the less limited access that is needed. 

Hope this helps. 

Regards Andy. 

I replaced that and still don't worked 

Ah crap. 😐 I was hoping that would have helped, not realising you'd already been down that route. 

It is the fan control resistor pack....the resistors between the lower speeds have failed and therefore no resistance to the motor on speed 4 so runs flat out

Replace the resistor pack and that will sort it

Thanks