QGIS raster calculator gives 'Nan'

With QGIS 2.14.3 I am attempting to convert a raster layer to a binary layer, using a certain threshold. With some layers I can use this formula in the Raster Calculator and get the expected output;

"raster@1"< 0.994 = 0 AND "raster@1"> 0.994 = 1

But when I try it with another layer the output is either all nan or all 0's. I've tried saving it in a different format (.img instead of .tif) as suggested in another answer here, but get the same result.

Is there a mistake I'm making with this?

Or an obvious reason it might give this output?

Or maybe the raster is just corrupted in some way?

(The imagery is the output from a long process, and confidential, so I can't share the actual file).