I have a Lennox furnace, cira 1972. Replaced thermal coupling. The pilot will light and the furnace will come on when I set the thermostat. Once the heat reaches the set temperature the furnace fan shuts off and the heat is reduced. Then the pilot goes out.
I replaced the thermal coupling and I understand that the tip should extend into the pilot light approximately 1/2 to 3/4 inches. It appears the it is only going in approximately 1/4 inches. I'm afraid that if I try to force it any further I might break either the gas valve or the flange that the coupling fits through. Help! I hate to call a repairman and pay out $200 plus for a repair.

You need to clean your pilot light sometimes you can do it by using a shop vac or a air hose first shut gas off take pilot tube off valve and blow air in the end sometimes you could put the vacuum hose over the pilot then reconnect turn gas on and lit.