Hi, This may sound silly, but we have recently bought a house with a combi boiler already installed and having never had one, I'm not sure what setting to have it on...though I'm not really that impressed so far...my last house had a separate boiler, separate hot water tank with immersion and gravity fed showers with a large cold tank in the roof...great hot water pressure...hot water 'instantly' and all day! But I digress! Anyway, nobody I know actually has the answer to my main question, so can anyone help? On the front of the boiler is a dial that reads 'Min' to 'Max' and inbetween it goes through settings I/II/III/IIII...I assume this increases the power/output of the boiler? The higher it is set the hotter the boilers 'btu' output? Am I correct? I have set the boiler running on 'Min' and the rads are hot and it gently warms the house, if I turn it up to 'III' the rads are much hotter and the house actually gets too warm upstairs! OK, now assuming I am right about the output...I then assumed if it throws out less heat on a lower setting it will use less gas! So, I set it to 'Min' (which is less than a 'I' setting) and ran it for 3 hours and logged the gas meter reading, it used 1.557m3 of gas....I then ran it on the higher 'III' setting for (again) 3 hours and it only used 1.485m3 of gas???? The house was far warmer in my second trial on the higher setting, we have no thermostatic rad valves and the same radiators were on in both trials...how and why is the gas consumption lower on the higher setting???? Thanks in advance to anyone who replies and can explain this.