Just thought i would add a bit to the scuttle panel cleaning and thermal fuse both of which are common problems, if cleaning out scuttle panel is neglected.
As mine was. Brought the car 2 weeks ago with heater not working so took a chance. Full main dealer service.
Had a look on here for problem and great advice on cleaning scuttle and thermal fuse replacement in How 2's. Descided to change the thermal fuse only and not the whole resistorpack.
1st day of rain while waiting for part to arrive and car flooded as mentioned in forum, yes i should of cleaned out the scuttle first, stupid mistake :-( water in front and back, drain blocked removed it and washed it before replacing.
The thermal fuse is a 240deg C and the old one needs to be cut off, i used a dremmel, Tin the legs on the resistor pack and tin the legs on the thermal fuse. You will need to create a heat sink to stop the fuse getting above 240deg when tinning and soldering so i wrapped mine in tissue soaked in water and held an ice cube on it to make sure,(best get another pair of hands for this) then solder in place.Cut off surplus fuse ends.
You can test with a multimeter should read 0 ohms across both pins.
The resistor pack is removed by sliding sideways and then it pulls out.
Check before refitting all. The resistor pack gets hot when working so hold on white plastic and not left on carpet.
Part from Maplins £0.82 part no: RA23A
Mine from ebay as Maplins were out of stock
ebay Cost £1.39
Thermal fuses are not directional.