Heater Problem

I've tried a search but it doesn't yield much.

Just bought my car and I've discovered the heater doesn't pump out heat.

- pipes leading toward the matrix are hot.

- bolt on pipe leading toward matrix is missing (so could have been looked at before).

- I can hear the motor making a noise as I adjust temperature.

- blower ok.

- temperature gauge normal.

- thermostat on order.

- coolant hot and clean.

Where do I begin looking next please?