A water pressure pump, often called a booster pump, increases the pressure and flow at your taps and showers by pushing water through the pipes with an electrically driven impeller. The right type depends on your plumbing: shower pumps are made for tank-fed hot and cold water, while weak mains pressure needs a mains booster, usually with a storage tank or accumulator, because water regulations limit how much a pump can draw straight from the mains.

Pressure or flow: know what you are fixing

Pressure and flow are not the same thing, and mixing them up is the most common reason people buy the wrong pump.

• Pressure is how hard the water is pushed, measured in bar. It decides how forceful a shower feels.
• Flow is how much water arrives, measured in litres per minute. It decides whether you can run a shower and a tap at the same time.

A plumber checks both. Pressure is read with a gauge on a tap. Flow is measured by timing how long a tap takes to fill a container of known size. A supply can have decent pressure with the taps shut but poor flow once water is moving, which usually points to a restriction in the pipe rather than a problem the water company can fix.

Before you look at pumps, rule out the simple causes:

1. Check the stop tap is fully open. A stop tap left half closed after work is a common culprit.
2. Clean shower heads and tap aerators. Hard water across much of Hertfordshire blocks them with scale.
3. Ask the neighbours. If the whole street is affected, contact your water supplier first.
4. Check for leaks. Turn off every tap and appliance and watch the water meter. If it moves, water is escaping somewhere, and our leak detection service can find it.
5. Consider the supply pipe. Older homes often have a narrow or corroded lead or iron supply pipe that limits flow however good the mains is.

Our guide to low water pressure in the whole house walks through these checks in more detail, and our general plumbing repairs team can carry them out for you.

How a water pressure pump works

Inside the pump, an electric motor spins an impeller that pushes water onwards at higher pressure. The pump starts automatically when you open a tap or shower, triggered either by a flow switch that senses water moving or by a pressure switch that senses the pressure dropping. When you close the outlet, it stops.

Pumps come in two main designs:

• Single impeller pumps boost one supply, for example the blended water leaving a mixer valve on its way to a single shower.
• Twin impeller pumps boost the hot and cold supplies separately, which is what a mixer shower fed from a tank and cylinder needs.

Manufacturers also distinguish between positive head and negative head pumps. A standard positive head pump needs some water to flow to it by gravity before it will start, so the tank must be high enough above the outlet. Where the shower is level with or above the cold water tank, for example in a loft conversion, a negative head (universal) pump is needed because there is little or no gravity flow to trigger it.

Types of water pressure pump

Type	Works with	What it does	Watch out for
Single impeller shower pump	Gravity-fed system, one shower	Boosts the blended supply to one shower	Must not be connected to the mains
Twin impeller shower pump	Gravity-fed hot water cylinder and cold tank	Boosts hot and cold to a mixer shower	Needs enough stored cold water to keep up
Whole-house pump	Gravity-fed system with several outlets	Boosts hot and cold to taps and showers around the house	Larger cold water tank often needed
Direct mains booster	Mains water with low flow	Gives a modest boost to the incoming supply	Limited to 12 litres per minute unless your water supplier agrees
Mains booster set with a break tank	Mains water with poor pressure or flow	Fills a tank from the mains, then pumps from the tank to the house	Needs space for the tank and pump
Accumulator	Mains water with good pressure but low flow	Stores water under pressure to top up the supply at busy times	Not a pump, but often the better answer

The rules on pumping from the mains

You cannot simply fit any pump to the incoming mains. Under the Water Supply (Water Fittings) Regulations, a pump connected directly to the supply pipe must not draw more than 12 litres per minute without the water supplier’s consent. Manufacturers of mains booster pumps design and limit their products to this for that reason. The same rules are there to stop one property pulling so hard on the main that it affects the neighbours’ supply.

Backflow protection matters too. Manufacturers typically require a double check valve before a mains booster so water cannot be drawn back into the public supply.

Standard shower pumps are designed for tank-fed systems only. They must not be connected to the mains cold supply, a combi boiler or an unvented hot water cylinder.

Where a home needs more than a direct booster can deliver, the usual solution is a break tank: the mains fills a storage tank through a float valve, and the pump draws from the tank. Because the pump is no longer pulling directly on the main, it can deliver much more.

Is a pump the right answer?

Sometimes a pump is exactly right, for example a mixer shower on a tank-fed system that only trickles. Sometimes it treats the symptom and not the cause.

• If the supply pipe is old and narrow, replacing it may give you the flow you need without a pump.
• If you have good mains pressure and a tank-fed system, an unvented cylinder gives mains pressure hot water to every outlet without a shower pump.
• If you have a combi boiler with poor flow, a pump will not make the boiler heat more water. Check the combi’s output against the flow you need first.
• If you are planning a new shower, choose it to suit your water system. Our shower installation team measures pressure and flow first.

Installation: what to expect

A pump should sit on a solid, level floor, usually near the hot water cylinder, on anti-vibration mounts with flexible hoses so noise does not carry through the house. It needs isolation valves so it can be serviced, and on tank-fed systems the pipework has to be arranged to avoid drawing air. The electrical supply is normally a fused spur, installed to the wiring regulations.

Pumps make some noise when they run. Positioning, mounting and pipe fixing make a large difference to how much you hear.

Common pump problems

What you notice	Likely cause
Pump starts on its own with every tap closed	A dripping tap, a leak or a faulty flow switch
Pump will not start	No power, not enough gravity flow to trigger it, or a failed switch
Loud running or vibration	Air in the system, poor mounting, or worn bearings
Surging or pulsing water	Air being drawn in, or a tank that cannot refill fast enough
Water under the pump	Worn seals or a failed connection
Shower runs hot and cold	Unbalanced supplies or a pump struggling on one side. See shower running hot and cold

What it costs with Vantage

In normal working hours there is no call-out fee. After the first hour, time is charged in half-hour steps, and parts are quoted before we fit them. Evening, weekend and overnight visits are charged at the out-of-hours rates. Every rate is published on our prices page, so you know what you will pay before we arrive.

We measure your pressure and flow first, so you only pay for a pump if a pump will actually solve the problem. A replacement shower pump is a smaller job than a mains booster set with a break tank, which needs more pipework and space.

Frequently asked questions

Can I put a pump on my mains water to increase pressure?

Only within the rules. A pump connected directly to the mains must not draw more than 12 litres per minute without your water supplier’s consent. For a bigger boost, the pump needs to draw from a break tank or accumulator instead.

Can I use a shower pump with a combi boiler?

No. Standard shower pumps are for tank-fed systems only. With a combi, the boiler’s flow rate and the mains supply decide your shower performance, so the answer is usually to improve the supply or choose a shower that suits it.

Why does my water pump keep turning on by itself?

Usually because water is moving somewhere, such as a dripping tap, a leaking valve or a running toilet, which the flow switch reads as demand. If there is no leak, the flow switch or pressure switch may be faulty.

Do water pressure pumps use a lot of electricity?

They only run while water is flowing, so for most homes the use is modest. A whole-house pump in a busy household runs more often than a single shower pump.

Will a pump help if my whole street has low pressure?

It may help your outlets, but contact your water supplier first, because a street-wide problem is theirs to investigate. Pumping harder from a weak main is also exactly what the water regulations are designed to limit.

Help in Hertfordshire, Bedfordshire and Cambridgeshire

If your showers are weak or your taps slow, our plumbers will measure what you have and recommend the fix that works, whether that is a pump, a new supply pipe or a different hot water system. See our general plumbing repairs service or call 01462 506374, answered 24 hours a day, 7 days a week.