The coffee machine's pressure system has no moving parts. It is the backpressure of the coffee in the basket that causes the build-up of steam pressure which drives the water through the coffee and provides the steam for the milk. So issues with that backpressure are a common source of low steam pressure. The back pressure depends on the fineness of the grind, the heat source, and the level of coffee in the basket. All three of these often need to be adjusted when you change the type of bean you are using or if the beans get old. If you are using the induction top then the beep at 8 minutes is about when your coffee should be extracted, plus or minus 20 seconds or so. If it is much earlier than this then the grind is too coarse or there isn't enough coffee. Much after and it shows the grind is too fine or there is too much coffee.
The starting point for a good grind is a normal espresso grind the same as a barista uses. Incidentally, if you are grinding the beans yourself you need a decent quality burr grinder (the Breville Smartgrinder is the cheapest we have come across) a blade grinder (like a spice grinder or blender) doesn't give you consistent grain size so you will get inconsistent results.
The coffee should always be double-dosed. That is, you pile the basket high, tap to get rid of the air, and then level with the top of the basket using something flat like a knife blade. Then tamp the coffee with 1-2kg pressure (not too hard). Then fill, level, and tamp a second time. At the end of the second dose, the coffee should sit within about a millimetre or so of the top of the basket, just below the radius on the edge. With well-ground coffee, you should be using the espresso basket, not the supermarket one (with fewer holes).
Another important thing is to not let the coffee run after it has passed its peak. A few minutes after the extraction starts you will hear a hissing sound from the head. This is an indication that the water has dropped below the pick-up in the boiler and steam is coming through instead of water. At this point the steam pressure will start to drop quite quickly so you won’t have much left for the milk and if you let it run until it stops the last extraction is stale and sour and will actually spoil the good coffee that you have collected. So best to heat the milk 2 or 3 minutes into the extraction. Once you’ve done that when you hear the hissing sound turn the heat off and release the remaining pressure from the wand into the air.