DIAGNOSIS The machine isn't reaching proper steam temperature, or you're activating it before it's fully ready. The Impress has a separate thermo-block for steam, and it needs time to heat up after switching from coffee mode.
FIX First, ensure you're in steam mode (the steam icon lit on the screen). Turn the steam knob to the on position. Wait. suggests 30 seconds, but for good pressure, wait until you see a steady, forceful jet of pure steam (not spitting water) from the wand—this can take closer to 45-60 seconds after the icon lights. Purge any initial water into the drip tray until it's just steam.
IF THAT DIDN'T WORK If it never gets to dry steam, the issue could be scale buildup in the steam thermostat or pathways. You might need to run a descaling cycle (using Breville's liquid descaler or another citric-acid based solution made for espresso machines).
HEADS UP Never leave the steam wand in the "on" position without purging it for more than a minute or two—it can overheat the thermo-block.