vaillant turbo max 282e?

Hi i have a vaillant turbo max 282e
The problem i am having is that when the boiler is running on central heating or hot water it goes off and then comes back on while i am in the shower the water goes cold then comes hot i have cleaned the hot water heat exchanger and also have replaced the diverter valve before this i had a friend of mine come around because i had to reset the boiler to get the heating or hot water on and he had adjusted the gas valve and since then i am having this problem all help will be great cheers guys.