I have an older Goodman air handler and the central heat won't turn off even when it exceeds the set temp, it will run and run until I turn off the thermostat. The a/c works fine. Any help here? I cvhanged the thermostat and still had the problem. Spoke to a friend who said it may be the sequencer but if so the thermostat should not turn the unit off. Any help here?

That sounds like a problem with a sensor in the heater. Perhaps the thermocouple, could be wrong though, I'm not extremely familiar with that kind of system.