Low Shower Pressure: Causes and Fixes

Is it the shower, the hot water or the whole house?

Before you touch the shower, run the kitchen cold tap. That tap is normally fed straight from the mains, so it tells you what the house is getting. Hold a 10-litre bucket under it and time how long it takes to fill. Under 60 seconds is 10 litres a minute or better, which is plenty for a mixer shower. If it takes two minutes or more, the weak shower is a symptom of a weak supply and the fix is on the supply side, covered in how to increase water pressure.

Then work out what kind of shower you have, because each type fails differently. An electric shower has a white box on the wall with a power switch and heats cold mains water itself. A mixer on a combi boiler takes both hot and cold at mains pressure. A mixer fed from a hot water cylinder with a cold tank in the loft is a gravity system, and its pressure depends only on how high the tank is. A power shower has a pump inside the unit, and some homes have a separate pump in the airing cupboard.

Finally, check whether it is hot, cold or both. Weak flow on hot only points at the boiler or cylinder side, which is a different problem covered in no hot water in the shower only. Weak flow at every temperature points at the head, the hose, the valve or the supply.

Checks you can do yourself, in order

Each of these takes minutes and needs no tools beyond a screwdriver. Stop as soon as the flow comes back.

• Unscrew the head from the hose and run the shower without it. If the flow is strong from the bare hose, the head is the problem. Soak it overnight in white vinegar or a kettle descaler, then rub the rubber nozzles with your thumb to push the scale out.
• Look inside the head’s inlet for a small plastic disc with a hole in it. That is a flow restrictor, fitted to many eco heads to hold flow at around 6 to 9 litres a minute. On a gravity system it can make the shower feel like a trickle.
• Run the shower with the hose held straight. Hoses fail inside: the liner collapses or kinks near the ends while the outer steel coil looks fine. A new hose typically costs £10 to £25.
• Find the service valves on the pipes feeding the shower, often behind a panel or in the airing cupboard. The slot should run along the pipe. A slot across the pipe, or at an angle, means the valve is partly shut.
• On a bar or concealed mixer, the hot and cold inlets usually have small mesh filters behind the wall connectors. With the water isolated, these can be unscrewed and rinsed. Check the manual first, because some are behind check valves that are easy to lose.

If the head and hose are fine and the flow is still weak at every temperature, stop taking things apart. The remaining causes are inside the valve or on the supply.

Why gravity showers are weak, and what the numbers mean

On a gravity system the only thing pushing water out of the head is the height of the cold tank above it. Each metre of height gives roughly 0.1 bar. A tank in the loft of a two-storey house with the shower on the first floor might give one metre or a little more, so 0.1 to 0.2 bar is common. That is enough to fill a bath but it makes a thin shower, and a shower on the top floor of a converted house can get almost nothing.

Many thermostatic mixers list a minimum working pressure in their fitting instructions, and some need more than a low loft tank can give. If yours was fitted recently and has always been weak, check the manual against your head of water before assuming a fault. The honest fixes are a valve designed for low pressure, raising the tank on a platform, or a pump.

A pump is the right answer only on this kind of system. It draws from the cylinder and the tank, not from the mains, and it needs a dedicated hot feed from the cylinder, usually through an Essex or Surrey flange, or it will pull air and cavitate. Whether one is worth it for your layout is covered in is a water pressure pump worth it.

Mains-fed showers: combi, unvented and electric

A combi boiler heats water as it passes, so the hot flow is limited by the boiler’s output. If the cold side is strong but the shower gets weaker as you turn it hotter, the boiler may have a blocked filter on its cold inlet or a scaled plate heat exchanger, both of which are boiler work. If both hot and cold are weak and the kitchen tap is weak too, the mains is the limit.

Never fit an ordinary shower pump to a combi or an unvented cylinder. They are designed for gravity supplies and pumping the mains is controlled. Under the Water Supply (Water Fittings) Regulations 1999, a pump or booster drawing more than 12 litres a minute connected directly or indirectly to a supply pipe, which includes most tank-fed shower pumps, must be notified to the water company before it is installed. If the mains itself is too weak, the usual route is a pumped accumulator or a break tank with a booster set, which is design work, not a quick swap.

An electric shower runs on cold mains and slows the flow on purpose to heat it. A 9.5 kW unit fed with winter mains water at around 5°C can only heat about 4 litres a minute to a comfortable temperature, and that is normal. A sudden drop is different. It usually means scale in the head, a blocked inlet filter at the back of the unit, or a failing solenoid valve. If yours has lost pressure along with other faults, see electric shower stopped working.

When it cannot wait, and what the plumber checks

Low pressure on its own is annoying rather than urgent, and the faults that are urgent are sorted by shower type in broken shower: can it wait?. It becomes urgent when the shower suddenly drops to a trickle and a ceiling below is damp, because a pipe feeding the shower may have split behind the wall; when pressure drops across the whole house at once, which can be a leak on your supply pipe; or when a power shower pump runs, hums or cycles on and off with no water coming out, which will burn the pump out. In the last case switch the pump off at its fused spur.

A plumber starts with a pressure and flow reading at an outside tap or the kitchen cold tap, and on a gravity system measures the head from the tank. They then work towards the shower: service valves, inlet filters and check valves, then the cartridge in a thermostatic valve, which scales up in hard water and can starve the outlet. A replacement cartridge is a common repair and the part typically costs £30 to £200 depending on the brand.

If the supply is the limit, they check the stopcock is fully open, look for a partly closed valve at the boundary or a pressure reducing valve set too low, and judge whether the pipe from the street is too small or corroded. Under the Guaranteed Standards Scheme, water companies measure low pressure against a reference level of seven metres static head, roughly 0.7 bar, in the communication pipe that feeds your property. If you are consistently below that, it is a matter for the water company rather than a plumber, as explained in low water pressure in my area.

For a visit, see our low water pressure repair service. The £60 call-out covers getting an engineer to you at any hour, and the repair price is agreed with you on site before any work starts. Full details of our plumbing call-out costs are on one page.