Talyllyn was the first order the company had delivered to north Wales and the first narrow gauge locomotive they had built with plate frames.

Early tests on the railway showed that the short wheelbase led to unacceptable vertical oscillation, and in January 1867 Talyllyn was returned to its manufacturer and fitted with a pair of trailing wheels, converting it into an 0-4-2ST.

Repairs and improvements were also made at Pendre over the years, including alterations to the cab, fitting of a footplate at the front of locomotive and of a sandbox.

By World War II it had fallen into a very poor state of repair, as it was the more popular of the two locomotives and was used more frequently.

In 1957 the locomotive was sent away to the Gibbons Brothers' Brierley Hill engineering works at Lenches Bridge in Pensnett[4] for a complete renewal.