Which Shower Pump Do I Need?

Updated July 2026 · Emergency Plumber Chelsea

First, check a pump is the right fix. A shower pump only belongs on a gravity-fed system, where a cold water storage tank in the loft or on a high shelf feeds a vented hot water cylinder. That set-up is common in Chelsea's older terraces and mansion flats, and it is often why the shower feels weak: the only pressure comes from the height of the tank above the shower. If you have a combi boiler or an unvented cylinder, your hot water is already at mains pressure, and connecting a pump to the mains supply is not allowed under the water fittings regulations. Our guide to mains pressure vs gravity-fed plumbing explains how to tell which system you have.

Positive head or negative head: the test that decides it. With the pump switched off or bypassed, turn the shower on to a warm mix. If water flows steadily out of the head, even weakly, you have positive head, because the bottom of the cold tank sits high enough above the shower for gravity to push water out. If you get a dribble that dies away or nothing at all, you have negative head. That is typical where the shower is on the top floor, in a loft conversion, or on the same level as the tank. A positive head pump starts when it senses water flowing. A negative head pump has a pressure switch that starts it as soon as you open the valve, because on its own no water would flow for it to detect. Fitting a positive head pump to a negative head shower is a common reason pumps fail to start.

Universal pumps and why they cost more. Some pumps are sold as universal, meaning they can work in either situation. They are useful when the test result is borderline, when the shower sits roughly level with the tank, or when you plan to move the bathroom later. They are usually more expensive than a pump built for one job, so it is worth doing the flow test first rather than defaulting to a universal model.

Twin impeller or single impeller. A twin impeller pump boosts the hot and cold supplies separately before they reach the shower valve. That is what most people need, because the usual arrangement is a mixer or thermostatic shower valve with separate hot and cold feeds. A single impeller pump boosts one supply, and is used after a blending valve, or on a single feed such as a bath filler. If you are unsure, look at the pipework: two pipes going into the shower valve normally means a twin pump. An electric shower is different again: it runs off the cold mains and should never be fed from a pump.

Choosing the bar rating. Pumps are sold by pressure, commonly from around 1.5 bar up to 3 or 4 bar. A higher rating gives a stronger, higher-flow shower, but it also empties your hot water cylinder faster and draws harder on the cold tank. A small cylinder with a big pump can run cold before the shower is finished, and an undersized cold tank can run low while the pump is working, which lets air into the pump. As a rough guide, match the pump to the shower head and to the storage you have. A standard shower head does not need the biggest pump on the shelf, and a drench or rainfall head may need a larger cylinder as well as a larger pump. If your shower already goes cold part way through, our guide to a shower running cold covers the usual causes.

One pump for the shower or one for the whole house. A shower pump boosts one outlet. A whole-house or multi-outlet pump sits near the cylinder and boosts several taps and showers, so a second bathroom or a kitchen tap also gets better flow. It suits larger Chelsea houses with bathrooms on several floors, but it needs a bigger pump, adequate pipe sizes and enough stored water to keep up. If you are thinking about a whole-house pump, it is worth comparing it with changing to an unvented cylinder, which our guide to vented vs unvented hot water cylinders weighs up.

How the pump is connected matters as much as which pump you buy. Many noisy or unreliable pumps are the right model fitted the wrong way. The hot supply to a pump should come from a dedicated connection on the cylinder, usually an Essex or Surrey flange, so that the pump is not sharing a pipe with other taps or drawing in air from the vent. The pump should sit on anti-vibration feet with flexible hoses, on a solid base, and away from a bedroom wall if possible, because pumps hum and click as they start and stop. It also needs a suitable fused electrical supply, which is electrical work and may involve an electrician.

Mansion blocks and shared tanks. In some mansion blocks the cold water tank is shared, or the freeholder or managing agent has rules about pumps and alterations to tanks. Pumping a shared supply can starve neighbours of water and is often not permitted. Check your lease or ask the managing agent before buying a pump for a flat. For weak mains pressure rather than a gravity-fed shower, see our guide to water pressure booster pumps.

Signs your existing pump needs replacing. A pump that keeps running after the shower is off, cycles on and off by itself, rattles or grinds, leaks from its casing, or only starts after you wiggle the valve is telling you something. Sometimes the fault is air in the pump or a sticking flow switch rather than a dead motor, so it is worth a diagnosis before replacing. If the pump is leaking, switch it off at its fused spur and turn off its isolation valves until someone can look at it.

When a pump is not the answer. If the problem is a blocked shower head, a clogged inlet filter or a partly closed isolation valve, a pump will not fix it. If your system is mains pressure, a pump is not allowed. And if you are renovating anyway, changing to an unvented cylinder or a system boiler can give strong showers everywhere without a pump. Our guide to improving low shower pressure walks through the cheaper checks first.

How we can help. Emergency Plumber Chelsea checks your system type, does the flow test, sizes the pump against your cylinder and tank, and fits it with the correct connections so it runs quietly and reliably. We also repair and replace failing pumps. There is no call-out fee on jobs over 3 hours. See our shower repairs service or call 020 3002 6667 for SW3, SW10, Knightsbridge, Sloane Square, South Kensington and Fulham.

Quick tips

• Do the flow test with the pump bypassed before buying: steady flow means positive head, no flow means negative head.
• Two pipes into the shower valve usually means you need a twin impeller pump.
• Never connect a shower pump to a combi boiler or unvented system; it is not allowed on mains supplies.
• Size the pump to your cylinder and cold tank, not just to the strongest shower you can find.
• In a mansion flat, check the lease or ask the managing agent before pumping a shared tank.

FAQs