Potterton Netaheat - no heating without hot water?

Boiler will only fire up when "hot water" selected on controller (EP2002). When hot water is on, radiators also heat up (whether or not the heating is set to "on" on the controller) but cool down when hot water is switched off, or when water is hot. Living room thermostat (Honeywell)setting doesn't seem to make any difference at all to heating levels.