Very old forced air furnace has thermocouple sitting in continuously lit pilot light. End of tcpl "wire" is screwed into a Baso pilot safety switch, model 850. It appears that the current from the tcpl energizes a small solenoid inside the Baso. I could not get the Baso to stay in the on position so this evening I replaced the tcpl, eventually twice. The first one worked for one cycle of the furnace, then the Baso tripped and could not be reset to on. I then installed the second tcpl, and it will occasionially let the burner gas come on for about a second, before the Baso would trip.
I can think of four possibilities as to what's wrong.
- The Baso needs replacing. The only reason I haven't done it is that it is and I can't see anything in it that could fail. It appears to be extremely simple.
- The pilot is under driving the tcpl. It gets the last 1/2" up to medium red.
- I have a bad connection where the tcpl is screwed into the Baso.
- The pilot is overheating and killing the tcpl.
I would appreciate if you would please hold the comments that any furnace with a pilot safety switch is an inefficient dinosaur and must be replaced. It is in an area with extemely moderate weather and our gas bill is less than $40 monthly in the middle of the winter, including gas water heater and stove. Thus, the break-even date on a new more efficient furnace would be... never. And, I like equipment that you can fix with a large hammer.
Any ideas as to what's wrong?
Henry