In 1925, the union's general secretary died, and Heap beat 26 other applicants in an exam set by the Amalgamated Weavers' Association, to win the post.
The union was in decline, but Heap led an organising campaign which doubled its membership in five years, and also improved its finances.
He also became active in the General Federation of Trade Unions (GFTU), and was a leading figure in its organising campaign of the late 1920s.
He followed the policy of his predecessor, Charles Kean, of engaging in committees with employers, and avoiding industrial action.
Membership grew slowly under his leadership, [2][3] In 1938, he was elected to the Management Committee of the GFTU, and he served as its chair in 1956 and 1957.