Mains water supplies and
how to improve.
Both Thermal Stores (including Heat Bank Thermal Stores) and Unvented Cylinders are limited in their performance by the mains water supply to a property.
Even is a hot water cylinder can provide 30 litres per minute of hot water, if the cold mains into the property is only 10 litres per minute, then you will only get 10 litres per minute out to taps.
Considering that a bath tap uses around 18 litres per minute, and a shower around 10 litres per minute, it soon becomes clear that to get 2 to 3 outlets running simultaneously requires a fairly decent mains supply.
There are 2 properties of the mains that should be looked at, and your mains water supplier is legally obliged to help you get readings:
The local water pressure is set by your water supplier. Legally they only have to guarantee 1 bar pressure (and 9 litres/minute flow), which is very low for most mains fed systems, and there is little you can do to help the situation. The ONLY way to improve water supply pressures is to install a cold water storage tank and a pump - it is illegal to pump the mains directly. The mains fills the tank via a ball float valve, and the pump forces this water to outlets at a higher pressure.
Given a set local water pressure, the flow rate into the property is dependant on the supply pipe sizes and lengths. This can be improved by replacing the supply pipe with a larger bore pipe. This can often be a very costly procedure however and may involve digging up driveways etc. Where there is a good local pressure and pipes are known to be small, this is the best solution, cost permitting.
A third option, and the cheapest, is to fit an accumulator. This is a steel vessel that stores mains water at the pressure it is supplied. Air within the steel vessel (trapped in a rubber diaphragm) is compressed by the mains water. When a tap is opened the water can rush out of the vessel to the tap - faster than the mains can get into the property. It is best imagined as like blowing up a balloon slowly and then letting the air out quickly. Accumulators only have one connection (like a balloon) and tee directly into the mains supply pipe, within the property. They cost around £200 to £300 and are very easy to install. The down-side is that they run out of water - once the vessel has empties you are back to the original mains supply flow rate. They also take up space; a vessel large enough to fill a bath would be 60cm diameter and nearly a metre tall.