Grant vortex pro external oil combi

I have this new installed in my house. The hot water is scalding. I have mixer raps indoors do it can be mixed down. But if you just turn s hot rap on it’s v dangerous. I understand I need to adjust the thermostatic blending valve. This has a white radiator type cap on it, but no markings. If I turn it the white plastic cap seems to just go round. Do I need to take this off as it’s a cover to adjust?

It should have been checked when the boiler was commissioned .

Is the dhw flow neon on all the time ? If so the
flow switch is stuck open
As said above the temp should have been checked, the white plastic cap can be removed and will expose an adjuster marked +and ~ try turning to lower temperature