Jessie had a great idea, the previous owner may have bypassed the heater core. But you say that you have had heat in the past, so that is not the case.

Please note that any time that air is coming through your vents, it passes through the heater core. There is no flap that controls the proportion of air that passes over it. All the air passes over it. If the core is cold, your air is cold, if the core is hot, the air is hot.

So the problem, at it's root, is no water flow through the heater core. Jessie's idea is a good one. Other possibilities are a totally clogged heater core, or the control valve is not opening. There is a valve that controls the water flow thru the core. It does go bad, but usually it fails in the "open" position so that you only get hot air.

The valve can be found near the gas pedal, and it has the one end of the linkage on it. The other end of the linkage is connected to the cold/hot slider control thing.

This is all assuming that you have enough coolant in your system. It's highly unlikely that it's an air lock type of problem, the air bleeds itself out pretty quickly under normal operation.

Greg