Low water pressure in the shower: causes and fixes

A weak shower is one of the most common complaints in older Bristol homes. The cause depends on how your hot water works, and in Bristol limescale is nearly always part of it. This guide helps you work out which problem you have and what fixes it.

Start with the shower head

Bristol Water says all water in its area is moderately hard to very hard, and it names showerheads among the places limescale builds up. Scale blocks the small holes in the head and narrows the hose.

1. Unscrew the head from the hose.
2. Run the shower without it for a few seconds. If the flow is strong, the head is the problem.
3. Soak the head in descaler or white vinegar, then rub the nozzles.
4. Check the hose for kinks and scale at the ends.

Many thermostatic shower valves also have small filters where the pipes enter. These clog with scale and debris. Cleaning them is a plumber job on most valves, as the water needs isolating.

Work out your system

Your system	How to spot it	Usual cause of a weak shower
Gravity: loft tank and hot water cylinder	Cold water tank in the loft, cylinder in an airing cupboard	Low head: the tank is not high enough above the shower
Combi boiler	No tanks, hot water heated on demand	Mains flow limited by supply pipe, scale in the combi
Unvented cylinder	Cylinder with a tundish and safety valves, no loft tank	Pressure reducing valve setting, scaled strainer
Electric shower	Its own unit on the wall, cold feed only	Scale in the unit, low mains flow

Gravity systems in Bishopston and Horfield

The Victorian and Edwardian terraces of Bishopston and Horfield often still run on gravity hot water. There is a cold tank in the loft feeding a cylinder below. Pressure at the shower depends on how far the tank sits above the shower head. In a two storey terrace with a bathroom on the first floor, that gap can be small. In loft conversions, where the shower is on the top floor, it can be almost nothing.

Fixes for a gravity system:

• A shower pump. Boosts pressure from the tank. It needs a suitable supply from the cylinder and tank and a spot for the pump, often in the airing cupboard.
• Raising the tank. Sometimes possible in a loft, but limited by roof height.
• Swapping to an unvented cylinder. Runs the whole hot water system at mains pressure, so showers and taps all improve. It needs good mains flow and must be fitted by a competent installer under Building Regulations Part G. See our hot water cylinders page.
• Swapping to a combi. Removes tanks and cylinder, but gives one outlet at a time a good flow. Suits smaller homes with one bathroom.

Combi boilers and mains flow

A combi can only deliver what the mains gives it. Many Bristol homes built before the 1970s still have an old lead supply pipe, according to Bristol Water, and many terraces were fed with a narrow pipe. The shower may be fine on its own but drop when someone runs a tap.

A standard shower pump cannot help here. The Water Supply (Water Fittings) Regulations 1999 restrict pumps connected straight to a mains supply pipe, and most need the water company’s consent. The usual fix is a better supply. A plumber can measure the flow at the kitchen tap to show whether the supply is the limit. Our guide to low water pressure in Bristol explains those checks.

Combi plate heat exchangers also scale up in hard water, which can reduce hot flow. That is a boiler service job, done by a Gas Safe registered engineer.

Electric showers

Electric showers heat cold mains water inside the unit. Scale builds on the element and in the outlet, which can drop the flow or make the water run cooler. Many have a small filter at the inlet. If the shower is old and scaled, replacement is often the better fix. Electric shower wiring in England falls under Part P of the Building Regulations. A new circuit or a bigger shower is notifiable work, so it must be done by an electrician registered with a competent person scheme or signed off by building control.

Mixer showers that run hot or cold

Sometimes the problem looks like low pressure but is really a balance problem. On a gravity system, the hot comes from the tank and the cold may come from the mains. A thermostatic mixer then struggles to blend them, and the flow drops or swings between hot and cold. This is common in older Bishopston bathrooms where a mains cold feed was added later. The fix is to feed both sides from the same pressure, or to fit a valve made for unequal pressures. A plumber can tell which you have by checking where each pipe comes from.

When the whole house is weak

If the taps are weak too, the problem is not the shower. Check:

• the inside stop tap is fully open
• Bristol Water’s incidents page for local problems
• your meter for a leak, using Bristol Water’s leak test steps

How a plumber helps

Our bathroom plumbing page explains how we approach shower jobs. A visit normally includes a flow test, checking the shower valve filters, identifying your system, and talking through which fix suits your home. In a Bishopston terrace, the right answer is often different for a family with one bathroom than for a shared house with an ensuite added in the loft.