I have a Bryant forced hot air which is about 30yrs old. The pilot stays lit, the blower works when it calls for heat but the jets ether won't ignite or run for about 15 seconds and shut off. At times it will fire up and then shut off. I was pointed by a friend it might be a faulty heat sensor I see there is a relay of something that is attached to the duct work above the jets. If a heat sensor would be anywhere I'm guessing it's there. There are wires leading to the control box and the gas valve. I can't seem to find any info on this dinosaur, so on to the question(s)

Is that what it is? Is this something that can be cleaned like others I've read about here?

Look for a flame sensor rod that is in thr flame ,that is the flame sensor, try cleaning with sandpaper