When my old back boiler burned its last, I hit the web to look at the 2 types of gas boiler that seemed more common: System Boilers and Combination Boilers.
The first type of gas boiler I read up on was the System Boiler, which offers roughly around 90% efficiency, placing it in Band A or B. These are the first and second best Band of boiler efficiency, meaning it is better for the environment AND your purse than say a Combination Boiler that typically sits at Band D. Though this immediately placed the System Boiler higher up in my estimations, the playing field soon levelled out when I realised that the System Boiler typically carried with it a higher price tag than the Combination. Back to square one!
I read that a Combination boiler does have quite a low water pressure rate, and the shower (for example) will run far slower if someone decides to start the washing up at the same time – not so good for a buys household like mine where we have 2 bathrooms and 4 people getting ready in the morning! As the System Boiler is invented for larger properties like mine, they are made to satisfy a big demand for hot water drawn from more than one room, so there is no drop in pressure when someone in another room turns on a tap. It was for this reason that the System Boiler won in the end.