Take a look at your expansion tank and check the water colour.
Your system needs cleaning, but the cause of that bright orange deposit needs investigation. It indicates highly oxygenated water. You may have a blocked cold feed.
Expansion tank water seems quite clear.
Follow the pipe down from the F&E (expansion) tank to where it tees in to the system. At this point see if you can feel any pull on a magnet. If there is magnetism it may be very slight.
If there is magnetism here this indicated that the cold feed into the sytem is blocked.
You could compare placing the magnet on a copper pipe to a tap to see how a clear pipe should feel!