Water Boosting

Unvented water systems require good pressure and flow from the incoming mains supply. Even if it’s good, is it sufficient for your usage requirements? For example, running multiple high demand outlets, multiple showers simultaneously or properties with shared mains.

Symptoms range from fluctuating flow in a shower to all other outlets being completely starved of water! This may occur when running a tap, taking a shower, using a washing machine or just flushing a toilet. If other outlets are affected, it may be down to insufficient pressure and/or flow. However, poor system design, incorrect pipe sizing or general cost cutting may also be a contributing factor!

In this situation, an Accumulator or Pump Set may provide the ideal solution. It also has other benefits! Both accumulators and pump sets serve the same purpose – to improve pressure and flow. However, there are important differences between the two. These are explained below.


Accumulators store water at mains pressure. They connect directly to the incoming mains supply, providing a buffer store of pressurised water. Similar to a rubber balloon filled with water!

When a system is designed and installed correctly, multiple outlets can be serviced at high pressure, high flow, with no drop in performance. Accumulators are well suited to properties with multiple bathrooms with simultaneous usage.

Accumulators store water up to the static pressure of the incoming water mains. Ideally, the incoming pressure should be above 2 bar, but the higher the better – ideally 6 bar or above. It’s often overlooked, but there are different types of accumulator and it’s important to use the correct one. If the pressure is available, you make full use of that! Many companies and installers incorrectly assume that the maximum pressure is 3 bar pressure!

Accumulator charging pump

If the incoming mains pressure is low, say 1.0 bar, then a charging pump may be used to ‘top-up’ the pressure. Any pump directly connected to the mains, may only pump a maximum of 12 litres per minute (Water Supply Regulations). Most unvented systems operate at around 3 bar pressure. For anything below this, a charging pump will help optimise performance.

Accumulators are extremely efficient and reliable

They simply use existing energy from the water supply to fill and pressurise a sealed hygienic container. This is stored under pressure as wholesome drinking water, until required. Accumulators are maintenance free, silent and and can be located more-or-less anywhere in the property.

Accumulator systems are modular

Several accumulators may be specified, or additional ones added at a later date. The total volume of water stored in all accumulators, must be sufficient to supply all water usage, at peak times. The accumulator will either be supplying water or being recharged. It can’t do both at the same time. Accumulators are generally the preferred choice where there is good static pressure, but poor flow rates.

We made the video below to give a crude demonstration of how well an accumulator works. This is only a small accumulator, but it clearly illustrates the real benefits available.


The video below demonstrates the benefit of an accumulator with a charging pump. The results are extremely impressive!
It first shows a single shower running off the mains. Then a second, third and forth are switched on. With four simultaenous showers, the flow reduces to a barely a dribble. Sounds familiar? Now switch on the accumulator, and you instantly have full flow to all four showers. When designed and sized correctly, accumulators can service as many outlets as required!

Pump Sets

Pump Sets consist of  a booster pump(s), a cold water tank, a small accumulator vessel, and some controls. They are ideal for situations where accumulators are not viable. Maybe due to higher pressure requirements or insufficient water pressure. Due to pump noise, these would generally be sited away from sleeping or quiet areas.

Larger installations may have two pumps to provided duty/assist operation, with both pumps only running together at maximum load. Additionally, the use of two pumps provides a level of redundancy should one of them fail. However, for the average size domestic property, a single pump system is often sufficient. The cold water tank must be sized to provide both hot and cold supplies at maximum usage.

Whereas accumulators make use of energy from the incoming mains, Pump Sets rely solely on the pumps to provide the pressure and flow to service the cold outlets and unvented cylinder. Pump sets would be the preference for larger properties with multiple high performance bathrooms.

An added benefit of using accumulator(s) or a pump set, is the availability of stored water in the event that the mains water supply is interrupted.

Please contact Apex Plumbing and Heating to discuss your requirements or to arrange a free on-site survey.

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