It is a generally accepted premise in logology that English words do not contain triplets of the same letter. As Ogden Nash points out, one does not expect to encounter English words containing LLL - or, for that matter, EEE or SSS. Recently, I had occasion to pursue a listing of tetragrams derived from the Second Edition of Webster's International Unabridged Dictionary and found that these triplets apparently do occur in English words.
Eckler, Faith W.
"On Searching for Three-L Lamas,"
Word Ways: Vol. 2
, Article 4.
Available at: http://digitalcommons.butler.edu/wordways/vol2/iss4/4