The Monster of Peladon - S11-E4
Plot hole: The temperature of the air being blown into the mines is controlled from the communications room when the Doctor needs to knock out The Ice Warriors. But conveniently, the ventilation system is controlled from the refinery when Eckersley needs to suffocate the miners.
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★