My furnace will not stay lit. I had the repair person in and they cleaned the señor. 2nd call and I needed a new furnace. Furnace came on and ran for 4 weeks. Can the build up on the señor be causing the same problem again? My furnace is a carrier weather maker 8000.

2nd call and i needed a new furnace

Why did they say you need a new furnace?

Usually a sensor will not get dirty in 4 weeks unless they did not clean it well enough to start with.

If cleaning the flame sensor didn't solve the problem, a new furnace definitely will. Whether you really need one or not. You must live near a lake, 'cause something smells fishy. Ask them for a specific description of the "terminal illness" and share it here.