Home ac heater unit heat wont come on?

Could be lots of things. If you have a standing pilot light, one that stays on all the time, the thermocouple may be bad. A thermocouple is a small rod that sits in the flame of the pilot light. It then runs to the gas valve. This produces a small amount of electricity that keeps the valve open to let the gas in. If the pilot light goes out it shuts the valve so the house doesn't blow up. Easy enough to replace. If the pilot light is still on and the furnace will not light, it has to be the thermocouple.

Check fuses at the furnace and in the panel.

Newer gas furnaces have a circuit board in them that can go bad. There are a dozen things that could keep it from working, it is just a process of elination.