If your furnace is running but not heating your house, there could be several possible reasons for this. Some common reasons include:
The thermostat is not set properly
The furnace filter is dirty or clogged
The furnace burners are dirty or clogged
The blower motor is not functioning properly
To diagnose the problem, it is best to contact a trained heating and cooling technician who can perform a thorough inspection of your furnace and determine the cause of the pr