ariston euro combi boiler?

I have a Ariston Euro Combi Boiler, it is over 10 years old. It still working fine but with a few issues.

Issue 1: If its on, then both the central heating and the hot water are on. Even if I just have the hot water set to be on.

Issue 2: It switches itself on and off all the time. It may run for 20mins then switch off for a few hours then back on again.

Issue 3: If its on the timer, it doesn't always switch it self off at the requested time. Not sure if this is the same as issue 2

These issues now mean we just switch it on when needed. We have a power shower so the heating was almost of the whole summer. This has now saved us a fortune on our bills, which is great but as we get closer to winter we would like this fixed. Any advice and Guidance would be welcome.