The answer depends entirely on whether the machine is new.
A new machine
Manufacturing oils, protective coatings and packing residue burn off during the first few heat cycles. A faint hot smell for the first two or three uses is normal.
Run two full tanks of water through — including the steam wand and hot-water tap — before making coffee, and discard the first couple of drinks.
An established machine
Rancid coffee oils. The commonest cause. Oils accumulate above the shower screen, in the basket and around the group, and they oxidise. When the machine heats, they smell.
Backflush with a cleaning tablet, soak the basket and portafilter, take off the shower screen. This is usually the whole answer.
Milk baked onto a steam wand produces a similar smell close to the wand.
Grounds on the heating element area on some bean-to-cup machines, where coffee escapes the brew unit into the housing. Worth opening the service door and looking.
When to stop
A smell of hot plastic or electrical burning — sharp, chemical, not food-like — means stop and unplug. That is insulation or wiring, and it is not something to run through.
The distinction is usually obvious once you are looking for it: coffee smells like coffee, even when it smells wrong.
Last reviewed 8 August 2026