Shower Power Booster

Easy | Efficient | Effective

Shower Power Booster

Easy | Efficient | Effective

I have just fitted my SPB but the flow is still poor? - Shower Power Booster

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If the shower power booster you have bought is not delivering the flow you expected there can be many things it could be so please contact us.

How much flow to expect may be determined by the mixer you have bought. Have you bought a tap or mixer designed for the UK? Is you mixer or tap designed for a gravity system?

With a good shower head, and no issues such as air in pipes etc, you can expect 6 litres a minute and a good shower. I am now going to make an assumption that you have not got 6 litres a minute and you want to know why.

Lets check that the pump is working first so here come my first ‘rule of thumb’. After many years of selling these pumps and visiting customers rule one is:-


An upstairs shower with one metre head before fitting the pump is increased to four metres head with a shower power booster so 3 litres a minute increases to 6 litres a minute. This is dependant on the flow you started with so 2 litres a minute without a pump might only increase to 4 litres a minute with the pump.

A downstairs shower with 4 metres head before fitting the pump is increased to 8 metres head with a shower power booster so 3 litres a minute increases to 4.5 litres a minute (50%).
You are always better to double boost the hot with a problem downstairs shower using a SP21S.

As with all rules of thumb, the flow increase is not a precise science, but it has proven a very good guide to what can be expected.

If you have just fitted the shower you should be able to find out its specification and there are two things it could be:-

The mixer is designed for balanced pressures
The mixer is designed for high pressures only


In designing a mixer which works well with low gravity pressures the designer may well compromise the ability of the mixer to deal with unbalanced pressure. A second SPB on the cold with a mixer which needs balanced pressure can be truly amazing. A pump I fitted for a customer in Norfolk had 2.5 litres a minute with just one pump on the hot got 8 litres a minute when a second pump on the cold was added. We think about one in five customers need a second pump on the hot and cold with 80% needing just the one pump on the hot.


Some mixers are designed for low and high pressures, others for high pressures only, but the very first thing to look for is an ‘eco water restrictor’. A small plastic grommet is often inserted into a shower head or shower mixer with the smallest of holes to reduce high pressures to low pressure. Check this. Also check to see if you have a filter before the tap or shower. These can often get blocked with shards of plastic or other debris when you first fit a tap or shower.

Some manufacturers sell you taps and mixers suitable only for high pressure systems. A mixer designed for a minimum of 1 bar pressure will only work in the basement of a three storey house with a cold water tank in the loft as it is only here where a gravity pressure of 1 bar is possible. Technically such a shower mixer could be described as suitable for gravity systems but in reality it works in very few cases. Some sell them for gravity systems but hidden in the specification is the words ‘with a suitable pump’.

If you buy a tap or mixer then the minimum pressure requirement is often stated and if its not stated, then its probably because they do not want to discourage you from buying.

Minimum pressure requirements:-

0.1 bars (1 metre head) – Very Good

0.2 bars (2 metres head) – OK

0.3 bars (3 metres head) – Avoid

1.0 bars (10 metres head) – only use in the basement of a 3 story town house.

If you think there is a problem, then here are some tips to help you identify if your shower mixer is challenging.

Google the name of the pump and the word ‘Specification” or ‘Technical Data’.
In the specification look for the words ‘minimum pressure’ and 0.1 bars is good, 0.2 bars is fair (but see below), 0.3 bars and above is challenging.

BEWARE of terms like ‘Flow Rate for open outlet’. This is great when you have a tap with an open outlet but you will get far less flow once you put on a shower head.
An example of this the Briston Frenzy which states a minimum head requirement of 0.2 metres and has a table of system pressure with an open outlet flow of 4.2 litres a minute at 0.2 bars.

Most buyers will not realise that 4.2 litres a minute is not a good shower by UK standards and that open flow means without a shower head.


You have an important decision to make and whilst the last thing you want to do is throw the mixer away and start again, it may be that replacing the tap or mixer is the best course of action. If you have a mixer that needs a minimum of 1 bar pressure (10 metres head), do you really want a noisy 3 KW power shower pump just to get a decent shower and replace it every 3 years?

If you need help finding the specification then you can ask us for further help and in some cases its a well known ‘lemon’ you might have.