renelt magan heating?

If you are certain that very hot water is actually circulating through the heater matrix ( both pipes almost too hot to touch) then maybe there are some flaps in the heater unit that aren't directing air through the matrix. See if you can look underneath the heater controls to see if the cables are still connected. PS the car temperature gauge will still function as usual - irrespective of what is going on in the heater.

John
December 2007