The small door on the side of the fiddley is to gain access to the scumming off valve which is designed to draw off any scum floating on top of the boiler water and eject it.
Jason arranges the chains for the crane to lift the new fiddley aboard. The lid on the top and the door on the back end are for gaining access to the boiler mountings, ie the main steam valve, the auxilliary valves port and starboard, the whistle valve, the safety valves and the low water level alarm.