be careful doing the “push up on the disc” trick. I’ve damaged a mechanical heat doing that.
What you have is a chemetronics heat detector. I haven’t tested mine in years, but I think I used a hair dryer or heat gun. you have to be very careful, too much heat will blow the FT element. hold the heat source more to the outside of the detector rather than at the disc. what markings are on the collector disc? A circle and/or a dot?