I have a older lennox (model # g1203-110 ) and change the thermocouple.The problem is that does not lite up when I turn on the heat. The fan works fine from the thermostat when I put the thermostat to fan on position and pilot stays on and I even hear it humming like it wants to go on but doesn't. Fire.What could be wrong? I am okay with schmatics and wire diagrams so if you can please show me where the problem is on the wiring diagram I can better understand your explanation on how to fix it and maybe fix it myself next time. Thank you much
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