My air condiction works fine bu when I put it on heat it won't come on at all no fan no noise or anything only thig I hear is a clicking on the circuit board that's it I have a lennox furnace
Thanks in advance

If this is an electric furnace then your contactor switch has gone bad and needs replaced. Call a service person to do this. Working with high voltage electrical current is not smart if you are an amateur. Refrigs are OK, but furnaces, no.