[binty]

Hi,
The heater/air on system has two drains as I recall.
Both in the passenger footwell.
One is from the fan at the left hand side and drains through the side of the car, the other from the aircon drip tray in the centre console area which drains through the front bulkhead.
I suspect this one is either damaged or blocked.

If you unclip the carpet on the transmission tunnel side and remove the plastic shield under the glove box, (2x Torx screws) you can pull the top corner of the carpet back and see it. It is a black rubber pipe about an inch in diameter and 5 inches long that pushes onto the white plastic of the aircon unit and exits via the front bulkhead.
May be worth pulling it off the aircon unit and pouring some water through to make sure it is flowing freely and also sealing firmly on the aircon unit. It is just a push fit at the aircon end but sealed into the bulkhead I think.
hope this helps.