How to do DIY

Shower Booster Pumps

A major problem confronting anyone wishing to install a shower in their home, either over a bath or in a separate cubicle, is ensuring sufficient water pressure to operate the shower satisfactorily. Most people expect a shower to deliver a strong invigorating spray rather than just a trickle of water.

All too often it is found that although water pressure is adequate at bath and basin taps, once a shower is fitted, with the spray head higher than other outlets, the pressure at the spray head is totally inadequate.

This is due to the spray head being too close to the water level in the cold water storage tank. Most showers will not perform unless there is a minimum height of 1 metre between the spray head and the water level in the tank. This is called the head of water. The higher the head the greater the water pressure.

DIY Projects - Installing a Shower Booster Pump

There are three ways to increase the pressure so that you obtain the shower that you desire.

ONE is to raise the cold water storage tank which feeds the hot water cylinder and the majority of cold water outlets, thus increasing the head. This involves building a platform in the loft and raising the tank to achieve the extra head or pressure. Plumbing pipework has to be extended and making this a laborious job. In many lofts such a change would not even be practical.

TWO is to fit an entirely independent instantaneous shower heater, fed with cold water from the rising main. The rising main will generally have considerably greater pressure. The heater itself can limit performance since the flow is controlled by the time it takes to heat the water to the required temperature. Whenever someone runs the tap in the kitchen, also fed from the rising main, or when the cold water storage tank needs replenishing, water pressure will also drop.
There is no way that water pressure can be boosted through a mains water fed instantaneous shower heater.

THREE, and by far the best answer, is to install a twin impeller shower booster pump.

The pumps are completely automatic once installed so you do not have to switch them on and off when you decide to have a shower. As soon as the controls to the shower are turned on and water flows through the pipework, an in-built flow sensor operates, switching on the pump. The only requirement here is that the unboosted flow rate from the shower spray head, when at its highest point, must be a minimum of 0.5 litres of water per minute. This is normally the case when the spray head at its highest point is not less than 225mm below the water level in the storage tank supplying both the hot and cold feeds.

See Diagram A.

Diagram A

Twin impeller pumps are particularly suitable for installations where access cannot be gained to pipework directly adjacent to the shower, between the mixer and sprayhead, because it is embedded in the walls, the situation in most homes. Connections are made to the supply hot and cold pipework before it reaches the mixer valve. The pumps can also be installed to boost supplies to other outlets in the house, such as the bath and basin shown in Diagram C.

Diagram C

Before you Start
There are a few requirements which must be adhered to if the Shower Booster
Pumps are to operate satisfactorily and safely. The existing water supply to the shower should be of equal pressure on the hot and cold side. This means that both hot and cold water must come from the same source, a cold water storage tank. Refer to Diagram A which indicates the pipe layout. In most systems it is usual for the same cold water storage tank to feed both the hot water cylinder and the cold taps, so pressure is normally equal. The cold supply should not come directly from a rising main since the pressure may fluctuate and will generally be greater than the pressure from a cold water storage tank.

Pipework should be 22mm as far as possible to reduce flow resistance. 22mm pipe is normally used for the supply from the cold storage tank to cold water feed pipes and the feed pipe to the hot water storage cylinder. Do not reduce to 15mm pipe until it becomes necessary.
The booster pump must always be sited with the pipe outlets pointing vertically upwards.
To prevent air being drawn down the hot water storage cylinder vent pipe and into the system, and to ensure that the shower has a hot water supply that cannot be affected by water being drawn off elsewhere, we strongly recommend that the hot supply to the pump is via a ‘Surrey Flange’ which is fitted to the top of the cylinder. Diagram B.

Diagram B

The Surrey Flange, shown in the above diagram shows the hot supply coming from the Surrey Flange rather than from a normal flow pipe at the top of the cylinder.

Flexible hoses must always be used to link both the incoming and outgoing pipes to the pump. Some pump vibration is inevitable and the flexible hoses help reduce the noise of such vibration and damage to the pump.

All plumbing work must comply with the requirements of Water Supply bye-laws. All electrical works MUST conform to BS767 the current IEE Wiring Regulations and Part P of Building Regulations. You are advised to check with your local authority’s Building Control Department, or an Authorised Competent Person, before starting. If in any doubt about electrical work, call in a qualified electrician.

Positioning the pump.
Position the pump so that it can be easily reached for servicing purposes this will save you time and trouble later on. The location of the pump will depend, to some extent, on where hot and cold feed pipes are accessible and also on whether the shower only is to be served or other outlets are to be boosted as well. If, for example, the pump is solely for use with the shower, the preferred method is to have a dedicated supply. If, however, other outlets do require boosting, the pump must be linked in to the main pipework before the branches to those outlets. See Diagram C.

With these factors in mind find a place for the pump where suitable connections can be made, ideally in the bottom of the airing cupboard. Under the bath or some similar location adjacent to the shower area is acceptable but it should not be sited where it could be splashed or touched.

The pump sits on rubber ‘buffer’ pads to reduce vibration noise, and must not be screwed down to the floor.

Use one end of the pump for the hot water, the other for the cold. When fitting this pump remember that you will require two sets of flexible pipe connectors. One flexible connector from each pair is used to connect to the pump inlets, the other for the connection to the outlets.

Pipe clips should not be used within 450mm of the pump, and plastic clips are recommended elsewhere. Metal pipe clips should be avoided.

Comprehensive fitting instructions are supplied with the pumps.

NOTE: Do not use jointing compounds, such as Boss White, since they will cause seals to leak.

If using soldered joints, do not allow flux to come into contact with plastic parts of the pump since the flux will cause corrosion and, eventually, leaks.

Electrical Connections
Electrical hazard will result if the pump is not correctly earthed. If in doubt - consult a qualified electrician or call in your local Electricity Company.

The pump must be connected to a 230 volt 50Hz supply with a switched spur fused at 5 amps. The switch must have a double pole disconnection with a separation gap of at least 3mm.

The connecting flex must be double insulated 3 core flex of 0.75mm2 area.


The first few times a pump is used, the insulating varnish used on the pump motor may give off an odour - this is perfectly normal and will diminish with use.


1. Read the instructions
2. Position the pump
3. Run pipework to and from the pump
4. Electrical connections

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