The pressure should be set at 1 Bar plus 0.1 of a Bar, for every extra full meter of head when static and cold. But this will have nothing to do with the hot water problem. As it would still work fine even if there were only 0.75 Bar in the system. If you have a system boiler then it is probably an undersized storage unit or the cylinder stat has not been set to 60 degrees or it is a faulty cylinder stat.
Or if you have a Combination boiler then it is probably not big enough for your hot water demands. Or a faulty thermistor. or even poor installation and commisiong proceedures.
Either way it is under warrenty and you should be calling the installers back to check it out, or phone the manufactures aftersales team and ask for them to take a look at it.