Hi, I have recently moved into a flat and was wondering how to use the boiler most efficiently to heat the radiators. I have an ecotech boiler and there is a setting to increase/decrease the temperature of the water (see pic). There is a thermostat in the living room, I put it on about 21 degrees. What difference does the temperature setting on the boiler make if the thermostat is at 21? Will I spend more on heating bills if its set higher, even though the thermostat stays on 21? Also if I have it turned to zero like in the photo, is that more/less efficient for the hot water in the shower and taps? Sorry if these are simple questions but I'm new to this. Thanks.