I have an older Sears Kennmore furnace, I'm guessing early 80's. Model # 867.763334 Furnace works great but intermittently does not work. When not working, only when I turn the power off and back on to the furnace will it work. Happens 3 times a week. Any ideas??

The furnace is locking out, there are many causes on why they will do this. Also Sears doesn't make any furnaces, see if you can find who did, there should be another manufacturers number, Like NUGK-100 would tell me it is a Tempstar, they made many of Sears furnaces. There should be a diagnostic light that flash's a code when the lock out occurs, see if you can find the number of flashes or the codes. Could simply be a dirty flame sensor. Does it have a pilot light? Is it always on? Does it light the pilot each ignition sequence with an electri spark, or a glowing ignitor?

The furnace is locking out, there are many causes on why they will do this. Also Sears doesn't make any furnaces, see if you can find who did, there should be another manufacturers number, Like NUGK-100 would tell me it is a Tempstar, they made many of Sears furnaces. There should be a diagnostic light that flash's a code when the lock out occurs, see if you can find the number of flashes or the codes. Could simply be a dirty flame sensor. Does it have a pilot light? Is it always on? Does it light the pilot each ignition sequence with an electri spark, or a glowing ignitor?

Everything on the manuals I have call it a Sears furnace. Model #867.763334 "pilot free gas-fired space saver furnaces" I can't find any lights on the circuit board panel. NO pilot light. A control box "direct spark igniter module". Also a fan limit control that is a box with a dial on it with temp ranges that looks like an old choke spring on a car. Any info is appreciated.

look at the plate inside the furnace, not the owners manual. It will usually have that sears number and more. Is it 80 or 90 percent efficient? Clean the flame sensor, if it is direct spark ignition there will be metal rods infront of the burners, one is for ignition the other is the flame sensor.

look at the plate inside the furnace, not the owners manual. It will usually have that sears number and more. Is it 80 or 90 percent efficient? Clean the flame sensor, if it is direct spark ignition there will be metal rods infront of the burners, one is for ignition the other is the flame sensor.
I found the MFG Model #, SUGB105AG01. I can't find who the actual manufacturer is.
You are right, the furnace goes into lockout mode. I can turn the thermostat down all the way for 1 minute and then turn it back up, the furnace kicks in. I'm going to try cleaning the flame sensor. Any other suggestions?

Is it 90%?

Is it 90%?
I have been all over that thing and I can't see where it says 80% or 90%. Built in 1978 though! The thing works great! I cleaned the flame sensor today, we'll see after a few days if that was the culprit.