Low Water Pressure — Common Causes and Fixes

Low water pressure in a UK home almost always traces to one of five things: a partially closed stopcock, a clogged filter on an appliance, a failed pressure-reducing valve, an airlock, or a supply-side problem. Diagnose by comparing the kitchen cold tap (raw mains) with the rest of the house.

Pressure complaints are one of our most common call-outs. The good news: most are quick to fix once you've narrowed down where the problem is.

First — diagnose where the pressure has gone

Before you start unscrewing things, work out whether the problem is the whole house, one tap, or hot only.

1. 1

   Test the kitchen cold tap

   In most UK homes this is the only tap fed directly from the mains. If it's strong, your mains pressure is fine and the problem is downstream.

2. 2

   Compare hot vs cold at the same outlet

   If cold is strong and hot is weak, the problem is on the hot side — cylinder, immersion feed, gravity-fed tank or scale build-up.

3. 3

   Check one tap vs the whole house

   If only one tap is weak, the problem is local — usually a clogged aerator or isolation valve part-closed. If everything is weak, the problem is upstream.

4. 4

   Ask a neighbour

   If they're also low, it's a supplier issue — check your water company's incident map.

The most common causes

Quick fixes you can do yourself

Open the stopcock fully

A part-closed stopcock is the single most common cause we see after recent plumbing work. Turn the stopcock fully anticlockwise until it stops, then back off a quarter turn (that prevents the valve seizing fully open). For more on locating and operating it, see our stopcock guide.

Clean the tap aerator

The little mesh insert in the end of a modern tap traps grit and scale. Unscrew it (most do by hand or with pliers wrapped in a cloth), tap the debris out, rinse and refit. Two minutes' work; routinely doubles the flow at a tap.

Check isolation valves

Most modern installations have a small screwdriver-slot isolation valve on the supply to each tap, toilet and appliance. The slot should sit in line with the pipe to be fully open. Across the pipe = closed.

Clear an airlock

1. 1

   Take a length of hose

   A washing-machine fill hose is ideal — it has standard tap fittings on both ends.

2. 2

   Connect cold to hot at the kitchen sink

   Tighten by hand so it can't blow off. Make sure both taps are turned off first.

3. 3

   Open the cold first, then the hot

   Mains pressure pushes upstream through the hot system, forcing the trapped air out. You'll hear it splutter then run clean.

4. 4

   Shut both taps and remove the hose

   Test the hot tap. If it's still weak, the airlock is deeper in the system and may need cross-flowing at another point.

When a PRV fails

A pressure-reducing valve (PRV) sits on your incoming main to bring high street pressure down to a steady ~3-3.5 bar for the house. They have a finite life — typically 10-15 years — and when the internal cartridge fails they either let full mains through (water hammer, banging pipes, dripping safety valves on cylinders) or, more commonly, gradually choke the flow.

Symptoms of a tired PRV:

• Slow, gradual drop in pressure across months or years.
• Pressure that varies wildly with time of day — high in the morning, weak in the evening.
• Sudden full-mains pressure when the cartridge fails open — see our water hammer guide.

Replacing a PRV is a clean job for a plumber and takes about an hour. It's not a DIY job — you need the right valve rating and the system has to be drained and repressurised correctly.

Low pressure on hot only

If cold is fine but hot is weak, the problem is on the hot circuit:

• Gravity-fed cylinder (cold tank in the loft, hot cylinder below) gives lower hot pressure by design — there's only a couple of metres of head. A shower booster pump or unvented conversion fixes it permanently.
• Scaled cylinder coil — in hard-water areas the heat-exchanger coil inside a cylinder furs up and chokes flow.
• Partially closed cylinder isolation — check the gate valve on the cold feed to the cylinder.
• TMV strainer — if hot is weak only through a TMV-fed outlet, the inlet strainer has scaled up.

Frequently Asked Questions

Related guides