1. Check the thermostat: Make sure the thermostat is set to "heat" mode and that the desired temperature is higher than the current room temperature. Also, make sure that the fan is turned on.
2. Check the circuit breaker: The circuit breaker that powers the AC/heater unit may have tripped. Reset the circuit breaker if it has tripped.
3. Check the air filter: A clogged air filter can restrict airflow and cause the unit to overheat, which can prevent the heat from coming on. Clean or replace the air filter if it is dirty.
4. Check the condensate drain: If the condensate drain is clogged, it can cause the unit to shut down. Check the condensate drain and clean it if necessary.
5. Check the refrigerant level: If the refrigerant level is too low, the unit will not be able to produce heat. You will need to call a qualified technician to check the refrigerant level and add more refrigerant if necessary.
6. Check the heat pump: If you have a heat pump, it may be in "defrost" mode. When in defrost mode, the heat pump will not produce heat. Wait until the heat pump finishes defrosting and then try to turn on the heat again.
7. Check the pilot light: If your unit has a pilot light, make sure it is lit. If the pilot light is not lit, you may need to relight it.
8. Check the blower motor: The blower motor is responsible for circulating the warm air throughout the house. If the blower motor is not working, the heat will not come on. You may need to call a qualified technician to check the blower motor and repair or replace it if necessary.
If you have checked all of these things and the heat still will not come on, you should call a qualified technician to diagnose and repair the problem.
