The heater tap.
Its on the RHS of the heater box, to get it out means removing the bottom of the black box, and then popping the heater core out. It cost me ~$A70 and was fixed in a day.
in between the two footwells there is a black plastic box with a flap in the bottom. While looking for this box, move the lever to adjust airflow from top to bottom (you following) and back again, you should see the flap moving.
There is two clips on each side (L+R) of the box, undo these and the bottom should pull straight down. Heater element should now be visible.
You will need to re bleed if you aren't careful, although it's probably a good idea to do it anyway.