lid tamper?

That would be the control panel lid tamper,

Have you removed it recently or has it had a knock or been damaged in some way?,

Check the panel, make sure the lid is seating correctly, I think the tamper switch is at the top RH corner on that scantronic panel.If you need to remove the lid from the panel to access the tamper spring, please remove the mains power from the panel first for your own safety.

e manno
July 2012