[Sam & Gromit]

I know exactly what I have do do, but I can't figure out HOW to do it. -.-
To be more precise:
I found out on my own that I have to make the mole people sweat by turning the boiler up, but for heaven's sake I can't find out how to turn the heat up! Clicking it just lets Sam talk a bit about it, but he does not change anything. And none of my items can be combined with it. And Future Vision doesn't let me choose it. (Though choosing the mole people delivers a related vision.)
I can't leave the place to look for some fire wood or other stuff, either. Is there a bug, or am I just missing something???

(I have already done everything else there is to do: All future vision objects have been examined, both the toy box and the zone creation thingy are plugged in, Skunkape is in the room but showing the paddle toy to him does not do anything as the sweat is missing.)