...warned that treadle is faulty (7)
I believe the answer is:
alerted
'warned' is the definition.
(alerting is a kind of warning)
'treadle is faulty' is the wordplay.
'is faulty' is an anagram indicator.
'treadle' is an anagram of 'ALERTED'.
'that' is the link.
(Other definitions for alerted that I've seen before include "Altered, having been put on guard" , "Put on guard, warned" , "Warned, made aware" , "Warned or aroused to a sense of danger" , "Put on guard, forewarned" .)