Slowly being eclipsed by the other types, these are the “header in the loft” type boilers. The entire system is fed by two open header tanks in the loft. For central heating, a pump outside the boiler is used to pump water to the radiators. The domestic hot water, meanwhile, is stored in a cylinder tank. This system has several drawbacks, including low water pressure at the taps nearest to the tank. Overall, it is the most costly and complicated of the three systems to install.