What should you check first if you have no leak and changed the thermostat in 97 escort and have no heat?

I had no heat in my escort either. A new thermostat, cooling system flush, new heater core, another new thermostat, ect. but nothing worked. Still only slightly warm air from the vents. The thermostat housing has a thermostat bypass in it. This bypass is always circulating coolant through your radiator. I plugged mine off with a thermostat gasket and now my car heats and blows hot air with no complications. Good luck.