The Steam Boiler is another of South Solitary Island's lesser-documented 'other' sites, an old steam boiler resting on the seabed near the island that most likely dates from the same 19th or early 20th century lighthouse-supply shipping era that produced the wreckage at the nearby Gantry site. Like Archie's Cave, it is not a headline attraction on Jetty Dive Centre's roster and is typically worked in as a variation for repeat visitors or groups looking for something beyond the well-known grey nurse shark and macro sites. Decades underwater have left the boiler heavily encrusted with sponges, corals and other marine growth, to the point where its original form is now more a suggestion within the surrounding rock and coral profile than a clearly readable piece of machinery — a common fate for small, isolated wreckage sites of this age on the NSW coast.

The site functions today essentially as a small artificial reef, sheltering wobbegong sharks, reef fish and the general invertebrate life typical of South Solitary Island, at a depth and in conditions broadly similar to the rest of the group's more sheltered moorings. Given the modest scale of the site and its status as a secondary rather than headline attraction, detailed published information is limited, and exact depth, position and condition should be treated as indicative pending direct confirmation from Jetty Dive Centre. For history-minded divers who have already covered the main South Solitary Island sites and want a look at another piece of the island's shipping past, the Steam Boiler is worth requesting, but it should not be the reason for booking a trip on its own.

Jetty Dive Centre departs from a public floating pontoon wharf on the Coffs Harbour boat harbour, opposite the Attitude Burgers building — check in first at 398 Harbour Drive, Coffs Harbour. It is roughly a 30-40 minute run out to South Solitary Island, 8 km offshore, in the dive centre's RIBs. Private boats launch at the Coffs Harbour public boat ramp inside the breakwall and follow the same course out past the harbour entrance.

South Solitary Island sits in open water 8 km off Coffs Harbour and is exposed to swell from the north-east through south-east; Jetty Dive Centre generally wants under about 1.5-2 m swell to run the outer moorings comfortably, switching to the more sheltered Split Solitary Island (only 20 minutes out) on rougher days. Visibility here is usually the best in the marine park given the distance from any river mouth, and the site's position at the boundary of tropical and temperate water means conditions can change quickly with wind shift. Summer (Nov-Apr) water is warmed by the East Australian Current to up to 26°C, bringing tropical fish, manta rays and, from December, leopard sharks; winter (May-Oct) cools to about 18°C but often gives calmer seas, giant cuttlefish and the peak grey nurse shark season (Jun-Nov, sometimes 30-60+ sharks on Manta Arch).

Humpback whales migrate past between April and November, peaking June-August northbound and September-November southbound. Currents can run strongly on the exposed north-eastern moorings (Manta Arch, Shark Gutters) and are much gentler on the sheltered north-western wall.

Descend to the boiler wreckage, explore the encrusted structure and surrounding reef for wobbegongs and reef fish, and circle back to the mooring or drop point for ascent.

Jetty Dive Centre (Coffs Harbour) runs South Solitary Island most days conditions allow, typically a double boat dive; it is the flagship site for the only major dive operator based in Coffs Harbour.