Yes, and how much depends on the machine.
On any machine
A brief flush after removing the portafilter clears loose grounds off the shower screen and stops them ending up in the next puck.
Two or three seconds. Do it every time.
On a heat exchanger, it is the temperature control
HX machines hold one boiler at steam temperature with a pipe of fresh water running through it. Water sitting in that pipe between shots keeps absorbing heat, so the first water out is far too hot.
The cooling flush dumps it. Owners learn their machine’s flush by feel — often by listening for the change in sound as the boiler valve opens.
Without it, an HX shot is scorched. With it, temperature is right. It is a routine and it is not optional.
On a single boiler
A brief flush stabilises the group temperature, particularly on the first shot. Long flushes drop the boiler below brew temperature and make things worse.
On a thermoblock
Very little benefit — there is no thermal reservoir to equalise. A short flush to clear grounds is enough.
What not to do
Flushing for twenty seconds on a single boiler because you read it somewhere. Know which machine you have.
Last reviewed 8 August 2026