Hi again,
Just noticed this on http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=518§ionId=25282

Causes of conductive hearing loss include:
middle ear infections (otitis media), build up of fluid in the middle ear (glue ear), blockage of the ear canal by earwax, injury to the eardrum, otosclerosis (a disorder of the middle ear), and rheumatoid arthritis
Tim