Elmwood sensor....

[mrcaptainbob]

Working on an old, CleanBurn waste oil furnace. I found this sensor does not have continuity, so I suspect it is no good. But how do I tell? I don't know if it's normally open or normally closed....the info on it is:
Elmwood 3004-5-8 L220 81/47
I did look up Elmwood anything and did not find what I need. Does the L220 mean that's it's heat limit? What might the 81/47 mean?

[SeattlePioneer]

Yes, it a limit switch that should open and shut off the burners at 220F.

[mrcaptainbob]

Limit sensor....

Thanks, Seattle Pioneer. That confirms my suspicion. But that leaves me with another question. How can I tell if it's normally open or normally closed? Also, are sensors like this used to control on/off situations? That is, to keep the item it's protecting from going past the temperature cutoff? In other words....how many cycles is a typical sensor good for?

[SeattlePioneer]

Limit switches are normally closed and open upon reaching the rated temperature. Some may be manual reset that remain closed until a button is pushed, otherwise they reset when the temperature declines twenty degrees or so below the rated maximum. They will typically cycle on and off as rated indefinitely.

[mrcaptainbob]

Sensor....

As I suspected, SeatllePioneer. Thanks for the confirmation.