If the Filter Size lights begin flashing, check the bean hopper before investigating the grinder or filter baskets. The machine may not recognise that the hopper is correctly installed. Make sure it is sitting properly on top of the grinder and is turned fully into its locked position.

If the hopper appears to be locked but the lights continue flashing, unlock and remove it before fitting it again. Position the hopper correctly over the grinder, seat it fully and rotate the locking mechanism into position. The Barista Express troubleshooting guidance specifically instructs you to correctly attach the bean hopper when the Filter Size LEDs flash.

The warning can be confusing because the lights are labelled Filter Size. However, on the Barista Express, the manual associates these LEDs flashing with the bean hopper, not an incorrectly installed 1 Cup or 2 Cup filter basket. Check the hopper before changing baskets or altering your coffee dose.

When refitting the hopper, make sure nothing is preventing it from seating and locking correctly. Don't force the locking mechanism. Remove the hopper, check that it can be positioned correctly on the grinder and then refit it in the normal locked position.

The Barista Express Impress uses a similar warning. Its alert guidance states that when the filter lights flash between the single and double basket size, the bean hopper isn't attached correctly. Check that the hopper is inserted correctly and locked into position before attempting to grind again.

If you've removed and correctly refitted the bean hopper but the Filter Size lights continue flashing, don't repeatedly force the hopper or grinder controls. Recheck the hopper installation carefully. The manuals identify incorrect hopper attachment as the cause of this particular warning; they do not provide a further user repair procedure for a warning that remains after correct installation.