Increased boiler make-up water consumption, increased opening of that boiler's feed water valve, and/or unusual control signals to that boiler's feed water valve.

Decreased superheated steam temperature from the effected boiler and reduction in boiler water chemical concentration.

Hissing noises from boiler casing in way of the superheater headers and/or evidence of water leaking from casing doors.

Increased boiler water make-up consumption and a loss of boiler water treatment chemical concentration in the effected boiler.