Green’s Dictionary of Slang

knuller n.

also gumbler
[OE cynllan, to knell; the old-fashioned sweep rang a bell to announce his progress along a street]

1. a chimney sweep who goes from house to house offering his services.

[UK]Hotten Dict. of Modern Sl. etc.
[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor II 357/1: The ‘knullers’ or ‘queriers,’ that is to say, those who solicit custom in an irregular manner, by knocking at the doors of houses.
[UK]Sl. Dict.

2. a clergyman.

[UK]Partridge DSUE (1984) 658: ca. 1860–1910.