If a thermostat woks fine for the cool operation is it correct to assume it should do the same for the heat? In other words, it it is a bad thermostat unit cool should not work either.
Thanks

With the digital/electronic thermostats in use today it could work on heat and not cool just for a example. Even the old style mechanical units could prove defective on one and not the other.

NOTE: thermostats are one of the most replaced parts in the HVAC system. 95% of the thermostats replaced are not defective. Thermostats last a long time.