What is a thermoblock espresso machine?

A thermoblock heats water on demand by passing it through a heated metal block — it heats up fast (30–60 seconds) but can struggle to maintain perfectly stable temperature during shot pulling. Thermoblock machines are common in entry-level and mid-range machines (Breville Bambino, De'Longhi Dedica). They're convenient and affordable but generally can't match the temperature stability of single or dual boiler machines at higher price points.