Is it a new boiler?? If it is the Wickes combi then it is most likely actually a Ferroli Combi just rebadged. The most common cause is that this particular boiler has no high point air bleed on the heating body and keeps going into overheat as it has got an airlock in the heating body. Other than messing around with the diverter valve for about 4 hours then forcing water through the heating body with an external pump on the flow and returns.
