Thermoblock, thermocoil or boiler?
The difference between a machine that is ready in three seconds and one that is ready in twenty minutes — and what you give up for the three seconds.
Thermoblock and thermocoil systems heat water on demand as it passes through, so they are ready in seconds but cannot brew and steam simultaneously. A boiler holds a reservoir of hot water: slower to start, more stable under load, and the only route to serious steam.
Published 2026-08-30 · Last reviewed 2026-08-30
Everything in an espresso machine that costs money is really about getting water to the right temperature and keeping it there. There are two ways to do it.
On demand
A thermoblock is a metal block with a channel through it and a heating element inside. Water enters cold and leaves hot, heated as it passes. There is almost no stored hot water, so the machine reaches temperature in seconds.
A thermocoil is the same idea with the water path formed as a coil inside the block. Breville uses the term on the Barista Express and pairs it with PID control, which is what makes it more stable than the name suggests.
Breville's ThermoJet is its current on-demand system, and the company states optimum extraction temperature in three seconds. That claim is a manufacturer figure and we record it as one — but the practical consequence is not in dispute: the Bambino is ready before you have finished weighing your beans.
Stored
A boiler holds a reservoir of water at temperature. It takes far longer to get there, and it can deliver steam continuously in a way a thermoblock struggles to, because there is a mass of hot water to draw on rather than a thin channel.
Thermal mass also stabilises brewing. A boiler machine's brew temperature does not sag as much through a long shot, and a brass boiler and group head — as on the Gaggia Classic Pro — hold heat between shots.
The steam consequence
This is the part that catches people out. On-demand heating is excellent at producing a shot and merely adequate at producing steam. A thermoblock machine can froth milk, and the automatic wand on a Bambino Plus does it well for one or two drinks — but it is switching between two modes with one heater, and it will not keep up with a round of four flat whites.
If milk in volume is the point, you want a boiler, and probably more than one.
The honest trade
| On demand | Boiler | |
|---|---|---|
| Ready in | Seconds | 15–25 minutes |
| Steam | Adequate, one or two drinks | Strong, sustained |
| Brew stability | Good with PID | Better, especially under load |
| Typical price | $250–$1,600 | $400–$3,000+ |
| Best for | Weekday espresso | Milk drinks, volume, control |
Neither is the better technology. A machine you use every morning beats a better machine you switch on twice a week.
Questions people actually ask
Is a thermoblock worse than a boiler?
For steam, generally yes -- there is less thermal mass to draw on. For getting a shot before work, a thermoblock is dramatically better. They are answers to different questions.
What is a thermocoil?
A coil of tubing embedded in a heated block of metal. Breville uses the term for the Barista Express and Barista Express Impress, where it is paired with PID control.