18 January 2013, Posted by Seamus Graham

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.

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 (an electric shower). 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.

THREE, and by far the best answer, is to install a twin impeller shower booster pump. There are four common types of twin impeller pumps available:

Plastic Twin Impeller Pumps 1.5 bar or 2 bar: 

● Increases flow rate to up to 16 litres per minute (1.5 bar) / 25 litres per minute (2 bar)

● Designed for intermittent use - 20 minutes on / 40 minutes off

● Transforms a new or existing shower into a power shower

● Fully automatic

● Increases the effective head by the equivalent of up to 12 metres (1.5 bar)/ 20 metres (2 bar)

● Quiet operation


High Performance Brass Twin Impeller Pumps 2 bar or 3 bar: 

● Increases flow rate to up to 25 litres per minute (2 bar)/40 litres per min (3 bar)

● Designed for frequent/continuous use in domestic and light commercial installations

● Increases the effective head by the equivalent of up to 20 metres (2 bar) / 30 metres (3 bar)

● Can power both a main bathroom and an en-suite

● Supplied with four high quality stainless steel braided hoses

● Adjustable flow switch sensitivity

● Quiet operation

● Integral stainless steel inlet filters

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 un-boosted 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.

Pump Fitting Figure 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 below.

Pump Fitting Figure C

Before you Start

There are a few requirements which must be adhered to if the Shower Booster Pump is 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, it is 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. The Surrey Flange stocked by Screwfix or Wickes and is supplied with full fitting instructions.

Pump Fitting Figure B 

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.The High Performance Brass Pumps are supplied with four high quality stainless steel braided hoses. You will require four 22mm compression connectors for the hose standpipe ends. 

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 above.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.

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

A pump must be earthed. Electrical hazard will result if the pump is not correctly earthed.

The pump must be connected to a 230 volt supply with a switched spur fused at 5 amps. The switch must have a double pole disconnection. The connecting flex must be double insulated 3 core flex of 0.75mm2 area or more.

Work Sequence: 

  1. Survey the current plumbing layout
  2. Decide on the best position for the pump
  3. Draw up a detailed shopping list and procure the bits.
  4. Run the pipe work to and from the pump
  5. Install electrical connections
  6. Commission and test the installation


Master Class - Extra bits  to know about shower booster pumps

Positive and Negative Head pumps

This is a term that you may have come across but misunderstanding still exists to exactly what it all means.

In a nutshell, the difference between the two is determined by whether the header tank is above or below the outlet point. If the header tank is above you have a positive head. If it's below the outlet you have a negative head.

In a gravity water system it goes without saying that water will only travel in the direction of gravity - downward. For this reason some people believe that if you take water down from the loft to a ground floor hot water cylinder, then back up to a first floor bathroom that water is indeed having to go up hill and that a negative head scenario exists. In this example this would be an incorrect conclusion. It is the relative position of the header tank to the outlet point. If the header in the loft is higher than the outlet point then a positive head exists even though the water travelled down to the ground floor before going back up to the outlet.

If indeed the outlet is higher than the header tank and a negative head exists you will require what's known as a negative head set up. In a negative head scenario things kind of happen in reverse. When you open your shower valve (or outlet - which could be a tap) water would rather run backward down the pipe to the header tank. SO... if you want your pump to activate automatically it needs to be equipped with a different type of sensor. Negative head pumps can usually be recognised by a canister that piggybacks the pump. This is part of the sensing system - not needed on positive head pumps. 

Standard Pump (positive head required)

Pump - Positive Head


Negative Head Pump

Pump - Negative Head

Connecting a shower pump to a hot water cylinder 

As mentioned, both the hot and cold feeds to a booster pump need to be gravity pressure supplies. The cold water feed can either be a dedicated cold supply direct from the header tank, or as is often the case, by teeing into the cold water feed to the hot water cylinder. Cold is simple enough. The hot water feed to the pump needs a little more consideration.

The normal hot water draw-off point is typically at the top of a hot water cylinder - right at the top, dead centre. If you simply pull your hot water from this point you may end up with a problem.

The reason: Hot water releases minute air bubbles. Ordinarily these rise to the top of the cylinder and vent out through the header tank in the loft. If you try taking water at the point where the bubbles are leaving the cylinder you are likely to pull them into the pump when it's running. This can cause a condition known as cavitation. In a nutshell, a big bubble of air forms at the low pressure zone ahead of the pump impellor. The condition can cause damage to the pump and will almost certainly generate some weird and wonderful noises - including squealing and banging!

The solutions:

1) If you intend to keep the present hot water cylinder you should consider using either a 'Surrey' or 'Essex' flange. This device screws into the top of the cylinder and creates two outlets. One becomes the normal outlet/vent, the other (being the shower take-off point) draws hot water from slightly lower in the cylinder, hence allowing the bubbles to pass on by.

2) If you intend to change the cylinder for any reason then make sure the new one has a dedicated shower take-off point. This will do the job of a flange type device. Shower take-offs shouldn't make the cylinder any more expensive, but you must ask for one to be fitted as they are not normally included.

Water Storage - System Capacity.

You might really like the experience associated with a powerful blast of water when taking a shower. Some people don't feel clean unless they feel a layer of skin has been removed during the event! But don't lose sight of how quickly you are emptying your water storage vessels as you shower.

A boosted shower will empty your system quicker. The bigger and more powerful the pump the quicker the system will empty. If you simply add a pump to your existing system you run the risk of potentially running it dry unless you do a few calculations. It is actually quite difficult to be precise with this because of various factors (how much water for example does your shower head deliver?). You will need to make certain guesstimations. The amount of water a shower pump will deliver will even be affected by how big the holes are in the shower head, and how many there are! Some how you need to calculate how big the header tank in the loft must be in order to provide an average of 10 minutes shower time. Yes, some people (especially teenagers) stand in the shower for longer, so you must either make provision for this or re-educate users. Some people find a timer on the show it use. Whatever you do and however you choose to do it, make sure you don't run your pump dry - this can cause it irreparable damage.  

Shower pump construction.

The materials from which a pump is manufactured will invariably influence the cost of the pump, but with good reason. Cheap shower pumps rely heavily on plastics in their construction. Whilst there is nothing wrong with plastics technology it happens to be a fact that pumps made mainly from plastic don't last as long as their more expensive counterparts. Pumps considered to be 'top end' products tend to be constructed from metal - especially the impellor housings that are often made of brass. It can often be a false economy to buy a cheap pump as the brass-bodied models can outlast them several times over. 

Noisy shower pumps.

A noisy pump can annoy you or drive you to despair! Pumps produce vibrations. This is a fact that cannot be ignored or negated. If you are looking for a vibration-free silent booster pump don't waste your time. Some pumps will vibrate more than others. You can probably guess that cheap pumps utilising cheaper materials and made with less refined manufacturing techniques are likely to vibrate more than their more expensive cousins.

As mentioned, vibration is the culprit. Quality materials and accurately machined components will minimise vibration and therefore noise output but will not get rid of it entirely. It is important to consider the transmission of vibration which is where the noise comes from.

Manufacturers of the more expensive brands of pump recognise this as a major issue. Pumps are therefore made from quality materials such a brass, motors are often of the 'induction type' that run more quietly and the foot upon which the pump stands is designed to absorb vibration - minimising transmission into the surrounding area.

Choosing a site for your shower pump.

Apart from all the operational reasons that will determine the most appropriate location for your pump, there is the issue of vibration. Even the quietest most expensive pumps will vibrate when in operation. It is therefore of paramount importance that you consider well how and where to put your little noise generator.

Place a shower booster pump directly on a timber floor and you might as well stand it on the sound box of a guitar. By it's hollow nature the guitar sound box amplifies small vibrations from the strings so you can hear them (by contrast a solid bodied electric guitar needs an amplifier or it can't be heard). A hollow wooden floor behaves in exactly the same way - amplifying vibrations. Don't do it - the noise could drive you crazy!

Whenever possible you should choose a location and/or stand your pump on materials where transmission of vibration is minimised. A small pad stone, maybe some sort of sandwich including rubber or polystyrene leaves might be considered a suitable way to insulate yourself from vibrations. Experiment but make sure the pump will be secure.

Don't be surprised if having ignored this advice you experience problems.

If you need a pump repaired, replaced or installed. Silver Saints, London's Handyman Service, can help.

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About the Author

Seamus Graham is the owner, MD, head honcho at Silver Saints. If he can't help you, no-one can...