[derekgas]

Long piperuns should be avoided where possible, most modern combis have a pre-heat system, so if the boiler is installed in the cylinder cupboard, the length of wait should be similar to that with a cylinder, a combi of any description is more efficient than storing water, it is worth noting that with a combi, you need good water pressure (cold), no matter how big the boiler is, it can only provide an equivalent amount of hot water that is available from the cold mains, if pressure is not good enough, then a hot tap opened downstairs will drop the pressure to an outlet being used upstairs at the same time, the only way to guarantee hot water throughout in this case is a 'y' plan system (keep the cylinder), but then the system efficiency is affected.