Manual Firing Mode - How Do I Tell The Fireman To Add More Coal?

I’ve just been opening and closing the firebox but it doesn’t seem to do a lot, getting no where near enough pressure.

What exactly am I meant to do/click to add more coal?

 

You ask him very very nicely, after all he has a spade and you don't

 

You have to looked him dead in the eyes, and speak the word’s “it’s the coal or you know. You.”

you’ll soon see their a dedicated and motivated employee.

 

*Stares at the firemen*
ADD MORE BLOODY COAL YOU DOUGHNUT