Glowworm 38cxi how to set lower base temperature

I have a Glowworm 38cxi that is working too well. Hot water is not a problem but when the Central Heating is set to the minimum user setting the overall temperature in the house is still too high and has to be controlled at individual radiators. The user instructions do not detail how to simply reduce the base temperature in the system. Any advice appreciated particularly with reference to the diagrams in the Installation manual http://www.glow-worm.co.uk/products/pdf/discontinued/boilers/CXI_range.pdf

You should have a timer and thermostat installed to shut off boiler once the house is at temperature!

Thanks LondonBoy. I am already using a timer and have individual termostats on each rad but this combi has a Central heating water temperature control knob (thermostat) and I would like to set the minimum at a lower temperature than it currently is in order to use the temperature to sometimes control an always on gentle background heat. I want to make the range of temperature controlled cooler - even in the recent cold spell I did not use more than 30% of the available temperature control range and I conclude that I will never turn this knob past 50% but I would like to be able to turn it down a little bit more.