Howzit all, im new here and joined up to seek some advice and of course see some great cars! ...... I've  recently had my air con re gassed and serviced and that is working a treat again, however, my heater isn't working at all. Had a mechanic have a quick check over near to where i work, he topped up coolant as was a little low and checked all pipes within engine bay to and from heater matrix, he said all seems fine within the bay as the correct pipes were at temperature once car was up to 90 degrees and the coolant levels now correct but still nothing at the vents at all? Could this be an air lock in the matrix? Can i ease the pipe form matrix near to battery that leads into the car, retracting it up past a small pin hole in the connection as I've read elsewhere and release pressure in the system?? Any help and advice would be really appreciated ....🤔

Could be an airlock or the ac control unit has had it. Are the rest of the functions working normally? 

Everything else seems fine Steve,  A/C working icy cold no hot air at max setting out of any vent at full engine temp nor when adjust air flow on dash to any position inc auto. How do i go about bleeding a potential air lock? Is it best left to Audi or can i release the hose that enters the car which i read about elsewhere that exposes a small bleed hole in the connecting aluminium nipple that accepts that rubber hose??? Any thoughts or knowledge of bleeding a matricx air lock on the B8 2.0 Tdi 2015 A4???   

If it were me I'd leave it for a garage to sort but I'm.not most mechanically minded. You could also consider a diagnostic check to see if any fault codes flag up regarding the system