I had an OEM digital thermostat get stuck on heat a few years ago, thankfully my furnace couldn't raise the temperature much above 90°, it was running continuously but it was also cold outside.
Replacing the thermostat fixed the issue. I called my HVAC people and they said that was the first time they heard of that happening with a solid-state thermostat.
A lot of thermostats, furnace motors, etc. are being made in China and Mexico now. We own an HVAC business and we have seen the quality of what were once high quality brands go way, way down.