If there is absolutely no heat, check the bowden cables(operating cables) are moving as they should, but in all likelyhood it will be a dash out job to renew matrix, around £30.
Just before you take the matrix out there is a metal bracket that secures the bottom of the dash under ash tray area, if you drill out the rivetts on this it makes it a lot easier, I just did this and put mine back with some large self tappers.
By the way the heaters are fairly crap anyway, got a new matrix in mine with a 2nd new stat 88C, but not a patch on other cars like my g/f's astra mk3, man that is roasting!!
As said fan circuit burning out is std kit on these, so would be best redone as would the fuel pump too.
tabetha