FURNACE WILL NOT KICK ON. REPLACED THERMOSTAT JUST TO BE SURE. THERMOSTAT WILL CLICK TO TURN ON FURNACE, BUT FURNACE WILL NOT IGNITE. PILOT IS LIT, THERMOCOUPLER WAS TAKEN OUT AND CLEANED, ALL WIRING IS WORKING. I DO NOT KNOW HOW TO TEST LIMIT OR FAN SWITCHES. ANY SUGGESTIONS?