Problem with netaheat profile 30e?

Hello, I have the above combi boiler and my problem is this. On the Honeywell control panel I can select the switch to heat the water, the boiler sparks and flame is seen. If I try it with the central heating switch, Nothing happens. I have checked the Thermostat (living room) and can see voltages, I have also checked the control panel, voltages seen. I have taken the cover off the boiler and can see voltages there when the central heating switch is on. Anybody have any ideas whats at fault here? Thanks in advance Martin Kite.