My A/C & heat system continues to run way after the Thermostat has reached the set temperature. I have a digital thermostat. I replaced the thermostat thinking that was the problem, but the new one does the same thing. Any ideas or reasons... This only began 4 days ago. Otherwise no problems at all in 2 years.

The question would be does the burner shut down and just the blower continue to run ? This could be a limit switch that needs adjusted, forcing your blower to run too long

My unit continues to Heat & Cool