Depending on how your system has been installed, there may well be a thermostat on the hot water cylinder to set the domestic hot water temperature. Check that is a) set correctly and b) working
You may like to consider getting one added if there is not.
There should be a room thermostat which turns the central heating pump on and off to control room temperature.
There will be a temperature control on the boiler. This governs the temperature of the heated water that goes round the radiators and the hot water cylinder primary circuit
Check the boiler manual for more details of how the system may/should be installed.
No manual? Download a copy.
You may also like to locate and download manuals for the room thermostat and the cylinder thermostat.