Arrived on site to perform furnace diagnostic on 2002 Lennox heater. Upon arrival client stated that gas company came out a few years ago and reset furnace. Began diagnostic and found that circuitboard molex plug is defective. Unit keeps thinking limits switch’s are open when they closed. Once pressure is applied to loose molex plug unit begans heating properly. System is from 2002 and have burn marks on control board. Client needs to talk with wife when she gets home and will give us a call for repair. Unit is operational upon departure