Room sealed boilers draw air from outside, open flue draw air from inside. Normally any open flued appliance above 7kw will require ventilation from outside
A gas pipe behind the plasterboard should also be fully encased in dot and dab. Electric cable should have a minimum of 25mm separation.
Check the regulations
Surprised to hear this about Worcester Bosch as they probably have the best repair/service, try getting in touch with the manager of the service department