A thermoblock is a block of metal with a channel through it and a heating element inside. Water flows through the channel and comes out hot. There is no reservoir of hot water — heating happens on demand.
The advantage: speed
A boiler has to bring a mass of water up to temperature and hold it there, which takes minutes. A thermoblock has to heat only the water passing through it, which takes seconds. The Sage Bambino reaches brew temperature in about three seconds from cold.
That changes behaviour more than it changes coffee. A machine that is ready instantly gets used on a weekday morning; a machine that needs twenty minutes gets skipped.
The disadvantage: stability
Because there is no thermal reservoir, output temperature depends on flow rate and on how long the element has been running. Over a long shot the temperature can drift, and the first shot after a break behaves differently from the third in a row.
Manufacturers compensate with electronics, and modern thermoblocks (Sage calls its version a thermojet) are considerably better than early ones. They are still less stable than a well-managed boiler.
Steam is the real weakness
Producing steam requires sustained energy, and a thermoblock has no stored heat to draw on. Steam pressure tends to be lower and to fade during a long texturing session. For one or two drinks it is fine; for six cappuccinos in a row it is not.
Who it suits
People who make one or two drinks and value not waiting. That is a large share of home users, and it is why the format dominates compact machines.
If you make many drinks at once, or you chase temperature precision on light roasts, a boiler machine is the better tool.
Questions people actually ask
Is a thermocoil the same thing?
Close. A thermocoil wraps a tube around or through a heated element; a thermoblock casts the channel into the block. Functionally they behave similarly.
Do thermoblocks scale up faster?
They have narrow channels, so scale narrows them proportionally sooner than it affects a large boiler. Filtering matters more on a thermoblock, not less.
Last reviewed 8 August 2026