Landyman,
The bimetallic strip should not be in contact with the spring loaded plunger above ~ 45degC.
I set the point at which the metal strip no longer made contact with the spring plate at around 42C. This was done on a bench, the idea is to isolate the spring and plate from the common, or the case of the wur. The bimetallic strip is also at common, so if you attach a wire to the spring, reassemble and measure for continuity between the case and the spring, when the circuit goes open (at 40-45 degrees) you know that above this temperature the heating element has no effect. I knocked my pin in another 0.1mm from where it was previously set with pressure by a shop. There may be other causes for what you're seeing, but this may be of interest to you. Oh, should mention that the teflon strips are very thin and should not affect the results, measure them for yourselves and see, you'll need one below the spring and one in the area where the pin goes into the plate.
Phil
