I have a Volkswagen Passat 1.9 TDI 1999 with a heater matrix problem I think (no heat. The car had a leak on the main cooling radiator so a mechanic put some sealant in last year. The car has had a new thermostat/water pump and been flushed. The heat control knob is working as I can feel the valve arm moving but I have not checked the heater valve to see if it is sezied. The pipes to the bulk head are both warm/hot but I am trying to avoid pulling the dash out.