“The pressure is low” covers a lot of different problems. A shower that has slowly turned to a trickle over a year is a different job from a whole house that lost pressure overnight. The first question we always ask is simple: is it one tap, or all of them?
One tap or the whole house
Open the cold tap in the kitchen, then a bathroom basin, then an outside tap if you have one. Compare how each one runs.
One tap or one shower is weak. The problem is at that outlet or in the short pipe feeding it. You can often fix this yourself.
Every tap is weak, hot and cold. The problem is on the way into the house: the main stop valve, the pressure-reducing valve, the supply pipe, or the supplier’s network.
Only the hot water is weak. Look at the water heater instead: a partly closed valve on its inlet, scale in the heater, or a mixing valve that needs attention.
The common causes, from simplest to hardest
A clogged aerator or shower head. The small mesh screen on the end of a tap and the holes in a shower head collect scale and grit. In hard-water areas this happens within a year or two. Unscrew the aerator, soak it and the shower head in white vinegar for an hour, rinse, and refit. If the flow comes back, you have found it.
A main stop valve left partly closed. After any plumbing work, a meter change, or a burst pipe, someone may have turned the main valve off and not opened it all the way again. A gate valve with a round wheel should turn fully anticlockwise. A lever valve should sit in line with the pipe. Old gate valves can also fail inside, so the handle turns but the gate stays half down.
A failing pressure-reducing valve. Many homes have a regulator just after the main valve that brings high street pressure down to a safe level. When one starts to fail, pressure often drops slowly, or swings between low and normal. They usually last 10 to 15 years. Replacing one is a job for a plumber.
Old galvanized steel pipes. Steel pipe rusts from the inside. Over decades the rust builds up and narrows a 20 mm pipe to the width of a pencil. If your home has grey threaded pipe and the pressure has been falling for years, this is a likely cause, and the only real fix is to replace the worst runs.
A hidden leak. Water escaping under a floor or in a wall takes pressure with it. A drop in pressure together with a higher water bill is a strong sign. Turn off every tap and watch the water meter for 30 minutes: if it moves, water is going somewhere.
The supplier. Work on the mains, high demand on summer evenings, or a home at the top of a hill on the end of the network can all give low pressure that is not yours to fix. Ask your neighbours. If their pressure is low too, call the water supplier.
Measure it before you guess
Two numbers tell you more than any description. You need a pressure gauge that screws onto a tap thread, sold in most hardware shops, and a bucket with litre marks.
Turn off every tap and appliance
No washing machine, dishwasher, or toilet filling. Any flow lowers the reading.
Fit the gauge to an outside tap or the washing machine tap
Use the tap closest to where the supply enters the house. Screw the gauge on by hand and open the tap fully.
Read the static pressure
Most homes sit between 2 and 4 bar (about 30 to 60 psi). Below 1.5 bar (about 22 psi) most showers feel weak. Above 5 bar (about 72 psi) the pressure is too high and puts strain on valves, hoses, and appliances.
Run a bucket flow test
Remove the gauge, put a bucket under the kitchen cold tap, open it fully, and time 30 seconds. Double the litres you collected to get litres per minute. A kitchen tap usually gives 8 to 12 litres per minute. Under 6 is low.
Compare the two numbers
Good pressure but poor flow points to a restriction: a clogged pipe, a half-closed valve, or narrow old pipe. Low pressure with low flow points to the regulator, the supply, or a leak.
Write both numbers down with the date. A plumber will ask for them first.
What you can check yourself
- Aerators and shower heads soaked and refitted
- Main stop valve fully open
- Valves under the sink and on the water heater fully open
- Neighbours asked whether their pressure is low too
- Static pressure and flow written down
- Water meter checked for movement with every tap off
If all of that checks out and the pressure is still low, the cause is usually inside a wall or under a floor. Our pipe repair visit starts with the same pressure and flow test, then traces the drop to the valve, regulator, or section of pipe that is causing it.
Written by
Tom B.
Drain and sewer technician
Runs the camera and the jetter across all four areas, and keeps the video of every line he inspects.
