My heaters blow cold on driver side hit on passenger side, passenger floor wet on 2005 Volkswagen Golf

I have replaced heater matrix but there is trapped air coming back up into my water tank it bubbles and overflows if i take the cap off after driver. Been told its the head but no creamy stuff on oil cap or dipstick and no white smoke. Also the air blocks from pipes have been cleared..any suggestions please?
Its a peugeot 307cc

Asked by for the 2005 Volkswagen Golf
possible heater issue.