Can't get hot water working, heating okay?

I've just moved house and have an Intergas Combi Compact Eco RF gas boiler with a separate Megaflow tank with expansion tank.

When I turn the heating timer to 'always on', the central heating fires up. My problem is that when I turn the hot water timer to on, the boiler does nothing.

Using the controls on the boiler, when I press the DWH / CH setting button, the green LED light for the central heating illuminates and I can change the temperature settings.

The instructions say that if I then press the settings button again, a different function LED will flash. I presume this means I should then be able to set the hot water settings but nothing on the boiler changes.

It therefore appears that the boiler cannot be set to run the hot water.

There is no sign of a separate boiler for hot water in the house so does anyone have any advice on what I can check for next. Thanks.