How to fix Ford Festiva Heater Problem?

The heater in my Ford Festiva will not blow our hot air?
I have checked and replaced hoses and the thermostat.
Both hoses connected to the heater core appear to be getting hot, which would suggest no blockage, ?
Any one have any other ideas?

Also, can any one advise, what allows/stops the hot air to come into the cab, once you have used the hot/cold selector on the dash......