I suspect that you have two separte issues: water leak, heater control fault
I advise you investigate the heater flap operation to ensure the flaps are moving on demand.
The door membrane is not fully sealed so water leaks in between the door interior panel and metal work.
The N/S/F door pad (panel) needs to be removed for inspection of the membrane seal (foam, metal or plastic panel depending on model/year)
Close doors and carry out water test (hose pipe over both doors until leek appears) this will show which door has the issue.
If metal panel remove all retaining bolts reseal seal strip on panel (mastic) or replace panel with new item, best result change panel.
If foam panel or plastic reseal sealing face with mastic or replace panel if ripped.
Carry out second water test to proof repair.
Refit door pad.
Note when doing water test only access vehicle through opposite side to inspect for leaks, easier if you are in car and have someone on the hose.
Thankyou for this, however, i need to know how to access the heater flaps. Also, The leak is not coming from water outside, there is a steady dripping coming from right underneath the dashboard in the passenger footwell. Please let me know if you have any further advice.
I have now resolved the problem. There was a damaged seal above the air intake causing the air filter to be wet and therefore very limited air could pass through. This also accounted for the dripping. Thankyou for trying to help but it appears that you did not provide the solution therefore i will not be paying the £11.