Radiators/Water cold but boiler is hot?

We've recently had the radiators taken off and put back on during some work which was being undertaken - prior to this heating and hot water working fine, however now the heating is turned on, the boiler (Vulcan Continental) is hot, but radiators remain cold as does water?

Note there are Potterton attachments to the hot water tank.

Does anyone know what may be the cause?