How to Increase Water Pressure in a House

Is it low pressure or low flow, and which system do you have?

Pressure is how hard the water pushes; flow is how much arrives each minute. A narrow, scaled pipe can show decent pressure on a gauge with no taps running and then collapse as soon as two taps open. Most complaints about “low pressure” are really low flow, and the fix is different, so measure both before spending money. Time how long the kitchen cold tap takes to fill a 10 litre bucket. Under a minute, so 10 litres a minute or more, is a reasonable baseline; a combi boiler or unvented cylinder often needs more, and its installation manual gives the minimum. Our guide to reading a water pressure gauge covers the pressure side.

Then work out how your water is fed. If you have a combi boiler or an unvented cylinder, every tap runs off the mains, so the mains is what matters. If you have a cold water tank in the loft and a hot water cylinder in an airing cupboard, your bathroom taps and shower are gravity-fed, and their pressure comes from the height of the tank above the outlet, about 0.1 bar for every metre. A shower one metre below the tank will always be feeble, whatever the mains is doing.

Finally, ask the neighbours. If the whole street is weak, see low water pressure in your area first, because the fix may belong to the water company.

Free fixes to try first

Go through these in order. Between them they solve a surprising share of low pressure call-outs, and none needs tools beyond a screwdriver.

• Open the internal stopcock fully by turning it anti-clockwise until it stops, then back a quarter turn. Stopcocks are often left half closed after a repair.
• Check every isolating valve: small valves with a screwdriver slot on the pipes to taps, toilets and appliances. The slot should run in line with the pipe.
• Unscrew tap aerators and the shower head, and soak them in white vinegar or descaler for a few hours. London’s hard water blocks them faster than most places.
• Look for a pressure reducing valve near the stopcock. If it has an adjusting screw and a gauge, it may simply be set low.
• If you have a water softener, check it is not left in bypass or stuck mid-regeneration, and that its pre-filter is clean.
• In a tank-fed home, lift the loft tank lid and check the tank is full and its outlet is not partly blocked with debris.

If the stopcock will not turn, or spins without effect, stop there. Forcing an old brass stopcock snaps the spindle and leaves you with no way to shut the water off.

Increasing pressure in a tank-fed house

Gravity systems are the easiest to improve, because the stored water in the tank and cylinder can be pumped, though any pump rated above 12 litres a minute still needs notifying to the water company first. The common upgrades are a shower pump, which boosts one shower, or a whole-house twin impeller pump, which boosts every hot and cold outlet fed from the tank. Stuart Turner and Salamander are the familiar names in UK homes. A “negative head” pump is the type needed where the shower head sits above the tank or level with it, for example in a loft conversion.

A pump cannot deliver more than the tank and cylinder can supply. A small loft tank with a slow float valve empties in the middle of a long pumped shower, so the tank and its feed may need upgrading at the same time. Our guide to whether a water pressure pump is worth it goes into sizing and noise.

Raising the loft tank by building a platform adds pressure in a small way, roughly 0.1 bar for each metre of extra height, and suits homes where a pump would be overkill.

Never fit a shower pump to a combi boiler or an unvented cylinder. Both run at mains pressure already, the manufacturers do not allow it, and pumping straight off the mains without the water company’s consent breaks the water fittings rules.

Increasing pressure in a mains-fed house

In a combi or unvented home, low flow is usually down to the supply pipe. Many older London houses are still fed by a half-inch lead or galvanised iron pipe from the boundary, sized for a single kitchen tap. Replacing it with a 25mm blue MDPE pipe, or a larger one for a big house, is the most effective single upgrade you can make, and it removes lead from your drinking water too, one of the problems old lead water pipes cause. Ask your water company whether it will replace its own section at the same time. As a market guide, replacing a supply pipe across a typical front garden commonly costs from several hundred pounds to a few thousand, depending on length, the surface on top and whether it can be moled under rather than dug.

Where the pipe is adequate but the mains itself is weak, there are two tools. A mains booster pump raises pressure from the supply. The Water Supply (Water Fittings) Regulations 1999 require the water company to be notified, and to consent, before any pump drawing more than 12 litres a minute is installed on the supply, directly or via a tank, whoever fits it. Pumping straight off the main can also lower pressure for your neighbours, which is why the consent exists.

The other is an accumulator: a pressurised vessel that stores mains water and releases it when several outlets open at once. It does not raise pressure; it holds flow up at peak times, which is often exactly the problem in a house with a combi and two bathrooms. Accumulators take up more space than a pump but have no motor, so they run silently, and they are not on the list of fittings that need the water company’s consent.

Should you switch to an unvented cylinder?

If you have a tank-fed system and a good mains supply, replacing the loft tank and old cylinder with an unvented cylinder gives mains pressure at every hot tap, without pumps. It only works if the mains has the flow to feed it, so a flow test comes first. Manufacturers quote a minimum incoming pressure and flow for each cylinder, and a weak supply means disappointing showers after the money is spent.

Unvented cylinders over 15 litres fall under Part G3 of the Building Regulations. They must be fitted by a competent person, which in practice means an installer with an unvented hot water qualification, and the installation must be notified to building control. The safety valves on these cylinders are there to stop a pressurised tank of hot water failing, so this is not a DIY job. The faults they tend to develop are covered in our hot water section.

What an engineer checks, and what it costs

On a low water pressure call-out, the engineer measures pressure and flow at the boundary stop tap and again inside at the stopcock. If the figures are good outside and poor inside, the loss is in your pipework, and they work along it: stopcock, pressure reducing valve, softener, filters, then the pipe itself. If the figures are poor at the boundary too, that is evidence to take to the water company.

Small fixes, such as replacing a half-seized stopcock, resetting or replacing a pressure reducing valve or clearing a blocked filter, are usually done on the first visit. Larger work, such as a new supply pipe, a pump or an accumulator, is priced and booked separately so you can compare. You pay the £60 call-out, and the repair price is agreed with you on site before any work starts. Full rates are on our emergency plumber prices page.