hi i have an audi a4 withe no heating had the car flushed twice and changed the water pump and thermostat been on pc they say i dont have a problem with head gasket it keep 90 all the time i have also changed the pipes to the heater radiators top pipe was hot bottom one cold...lost me unless its the heater radiator

this one is preaty easy to solve. All audi's and vw engines are completly sealed presurized systems. Removeing the water pump breaks this seal and causes bubbles in the cooling system to form which in turn end up causing your heat to stop working. Have the antifreeze lines bleed from the bleeder valve. This will fix your issue by getting the bubbles out of your system. you can also try to keep the cap off your coolant tank.. run the car and milk the upper radiator hose a little to try and get the air out.. do this with temp hi fan speed low.. will take some time, but it should get any air out of the system They both do the same. Also check the hoses that lead to the heater core when your car is warmed up. make sure both lines are hot while hte heater is at full blast full heat. Other issues that can cause this is a cloged heater core.