First, did you try my suggestion? You said you would try it last night, but you didn't say if it worked or not.
Since you say that only one of the three failure modes is appropriate (or the "fourth", which would be no text), I'd suggest using a combo box that would refer to a lookup table (called "FailureStates") that would contain two columns: FailureID (autonumber column), and FailureText. Set it up so the first record is blank in FailureText with a FailureID of 1, then add the other three text descriptions. Or you could have two "none failure" records, one with the text "Not a critical instrument" and the second either blank or "Did not fail", that way you would in one field indicate if an instrument is critical or not (value over 1 if a critical instrument) and, if a critical instrument, if it failed (value over 2) and if it did fail, the failure category.
On your form create a combo box for FailureID that would only display the text and would default to a FailureID of 1 (for blank text). You could, if you want, save this in your data table with the instrument history.
When you print your calibration sheets, just print the text that goes with the value of FailureID based on the lookup table. An added advantage of this approach is that when "management" decides that the text should say "Failed when closed" rather than "FailClose", all you have to do is change the text in the lookup table once. Then all reports you print after that will display the new "better" text.