Help Please, I have a 23 yr. old Lennox, model G2003E-50-3 and it's time to upgrade but money is tight right now. When I turn the heater on, ( *click-click-click*) the pilot will light but the gas control relay won't open the valve (*click-woooosh*) for the main heat. There's a multi-circut box mount on side panel with about 8 wires out of it, each connected to it's own spot (ex. PV, MV, MV/PV, Sense, TR, TH ) and on main gas control valve a small circuit relay with 3 connection slots, an M, a C, and a P, From first box I mentioned, a RED wire goes from slot MV to gas conrtol relay slot M. A BLUE wire goes from slot MV/PV to gas control relay slot C. an ORANGE wire goes from slot PV to gas control relay slot P and then the ORANGE wire continues down to a main circuit board. Whew! Don't know what to replace 1st. Help me get my *WOOOOSSH* back. Thanks