Can I change the dip switch setting on my Siemens RWB9?

I have a siemens RWB9 and I cannot get the Central Heating to come on without the hot water. Both lights come on when I turn the central heating on. From reading the manual I think I need to change the dip switch setting. It's currently set to 3 prog 10 mode but i'd prefer it to be 2 prog 16 mode. Can I change this setting? If so how do I do this? I used to be able to get them to work independantly so someone must have changed a setting somewhere along the line.
Any help would be appreciated.