My son's astra has perennial problems with heater circuit. Has an earthing fault that causes the whole thing to fuse every now and then. Last time it fused the whole switch stopped working. Easy enough to change the switch, it prises out of the dash with a screwdriver, I use a fine flathead wrapped in washcloth to stop damage on the finish. Then simply unplug wires on the switch back and plug onto replacement in same order. 'Pop' it back into the dash and its done. Switch costs about 25 squid or whatever your local scrappy charges.
If you suspect that (as with old german made models) one of the retaining clips has been melted to stop it being popped out then you can go up the back by taking off the fairing and going in behind to check but its a bit of a hassle.
hope this helps-