my breville barista express is flashing the clean/descale light, what does that mean?

A flashing Clean/Descale light means it's time for a back-flushing cleaning cycle, not a descale. A solid light means descaling is required.

1. Insert the 1 CUP filter basket into the portafilter, then the supplied cleaning disc, followed by 1 cleaning tablet.
2. Lock the portafilter into the group head and place a large container under the spouts.
3. Fill the water tank with cold water and ensure the drip tray is empty.
4. Press the POWER button to switch the machine off.
5. Press and hold the 1 CUP, 2 CUP, and POWER buttons together for about 10 seconds.
6. The cycle runs for about 5 minutes. Water will flow intermittently from the portafilter. Two beeps signal completion.
7. Remove the portafilter and check that the tablet has fully dissolved. If not, repeat the cycle.

IF THAT DIDN'T WORK: If the light is solid (not flashing), then descaling is required. You'll need a Breville Descaling powder sachet dissolved in 34 fl oz (1L) of water to fill the tank, then enter Descale mode by holding the 2 CUP and POWER buttons simultaneously.

HEADS UP: Never remove or completely empty the water tank during a descaling cycle. The machine will turn off automatically if there's no action for 5 minutes in descale mode.