Performed furnace clean and tune; inspected the exhaust and intake PVC ensuring all connections were secured, removed and cleaned the burners along with the flame sensor, cycled the system on and performed a combustion test verifying no CO in the airstream, as well as cycled on the humidifier found that the water valve was stuck closed due to the age and cost to repair I recommend replacing the humidifier. This system is currently operating normal and heating at 48 degrees at this time. Job complete