Afternoon. My mum has an Audi A4 B7 Cabriolet / convertible 1.8T 2007. Car is sitting at 125,000 miles. 

 

The heating wasn't working for a good while so I've drained the coolant, put a hose through the top heater pipe to clear it out. Topped it up, bled the air out via the bleed nipple on the top hose and now the car is getting heat on the low fan speed setting. top hose is warm now too so I'm confident the heater matrix is fine (unless someone tells me otherwise haha).

 

Only problem is that when you turn the fan speed up it's no longer hot. Feels like maybe the flaps aren't turning as they should for the fan speed or something? Not sure but I get the feeling it's still feeding hot air but it's overpowered by colder air.

 

Any info is much appreciated.

 

If the heater hoses are only getting warm, rather than hot, I'd say you still have a partial blockage in the matrix.

2 hours ago, cliffcoggin said:

If the heater hoses are only getting warm, rather than hot, I'd say you still have a partial blockage in the matrix.

I wouldn't be surprised if that was the case but would you say that the top hose should be about as hot as the rest of the coolant hoses in the engine bay? Next chance I get I'll check again. 

Anything else it could be if it isn't the matrix?

Yes, the same temperature as the main hoses off the radiator. Try reverse flushing the heater matrix with mains pressure water. If that does not work the matrix will probably need to be renewed.