I have a combi boiler system. Recently when the water is turned on there is a very loud banging noise from the pipes. Is this something I can fix myself?

Sounds like water hammer.

There are normally three ways to fix it. Find a way to turn the water on very gently (normally involves fitting a valve somewhere), reduce the water pressure, or brace the pipes in the middle of any un-suspended runs.

By far the easiest fix for most people is to reduce the pressure. On mains fed systems, you just adjust the main stop-valve to throttle it. If it's just the cold taps/toilet valves causing the problem, turn down (but not off) the main stop cock. Never owned a combi boiler, so couldn't say for certain, but assume reducing the inlet pressure would do the trick for hot water too