Whilst working on the co-op sequel (KiR: Together) I found a sneaky little bug ('=-' instead of '-=' ah how glorious) which caused an awakened Doll to instantly remove all heat from the Boiler when sabotaging it.
With the fix it's now as it should be: when a Doll sabotages the Boiler it takes one coal out of the Boiler, removing slightly more than the amount of heat one coal would give.

By the way: the Keep It Running: Together Steam store page is awaiting approval by Valve, so it will be online one of these days!