Apex Plumbing and Heating

Specialists in hot water and heating systems

Accumulators and Pump Sets

Unvented water systems rely on a combination of water pressure and flow to meet the demands of the modern household. With some properties, the mains water supply may simply be insufficient to ‘power’ an unvented water system to meet the users expectations.

The symptoms are typically a decrease in performance when multiple outlets are in use. For example, running a tap or shower, using a washing machine or flushing a toilet, shouldn’t affect other outlets, but if it does, this may be due to the incoming pressure or flow.

Also, larger properties with multiple bathrooms often suffer with poor performance when using several bathrooms simultaneously. This is often down to poor system design, incorrect pipe sizing or simply cost cutting!

In these situations an Accumulator or Pump Set may provide the ideal solution, together with some additional benefits! These are ideal for properties with old or shared mains, multi bathrooms or multiple high demand outlets. Both accumulators and pump sets serve the same purpose, but there are notable differences between the two, which are explained below.


Accumulators store water at mains pressure; they connect directly to the incoming mains supply and provide a buffer store of pressurised water – similar to a rubber balloon filled with water!

Providing the system is designed and installed correctly, multiple outlets can be serviced, at high pressure with no drop in performance. These are ideally suited for properties with multiple bathrooms with simultaneous usage.

Accumulators store water up to the static pressure of the incoming water mains, but for properties where the incoming mains pressure is low, say 1.0 bar, then a charging pump may be required to ‘top-up’ the pressure. As most unvented systems operate at around 3 bar pressure, anything below this would benefit from a charging pump to optimise the performance.

Accumulators are very efficient and reliable; they simply use energy from the water supply to fill and pressurise a sealed hygienic container. This is then held under pressure as wholesome drinking water, until required at one or more outlets. Accumulators are maintenance free, silent and and can be located more-or-less anywhere in the property.

Accumulators systems are modular; several may be specified or additional ones may be added at a later date, if necessary. Accumulators would generally be the preferred choice where there is good static pressure, but poor flow rates.

Boost a Main

The video below demonstrates the benefit of an accumulator with a charging pump; the results are extremely impressive!
This shows a single shower, and then a second, third and forth are switched on, and the flow reverts to a barely a dribble. 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 are made up of booster pump(s), a cold water tank, a small accumulator vessel, and some controls. They are ideal for situations where an accumulator is unsuitable, maybe due to higher pressure requirements in large or tall properties. Due to pump noise, these would generally be sited away from sleeping or quiet areas.

Typically, two pumps are used 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 pump fail – this is very important. 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 outlets and unvented cylinder. This may be the preferred option for larger properties that require higher pressures with a high usage demand.

Pump sets would be the preference for larger properties with multiple high performance bathrooms.

An added benefit of having 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.

Call Now Button