Audi Repair: Audi a4 1.8t cabriolet heater blowing cold air, audi a4, fan works

Question
i have an Audi a4 1.8t cabriolet on an 04 plate. the  heater is blowing cold air and will not blow warm, fan works etc, any ideas for what to look at,, ta

Answer
hello
Air in the system??? , check both hoses , next to the battery, which are going inside the car . One is IN , one OUT to the heater core .If both of them are hot ( almost same temp.) it means coolant goes inside .
My next step is to check for fault in A/C control head. maybe one of the flap is stuck close.
good luck             Greg