If your shower dribbles or a combi boiler struggles, mains water pressure is a likely suspect. The good news is that you can test it yourself, and in many cases the fix is simple.
What is normal?
Pressure is measured in bar. In UK homes it commonly falls somewhere between about 1.5 and 4 bar, though it varies by area, time of day and the height of your home above the supply. Water companies have a minimum standard to meet at the boundary of your property, roughly 0.7 bar at a stated flow rate. Below that, you may be entitled to raise it with them.
Pressure is only half the story. Flow rate, how many litres a minute you can draw, matters just as much. A decent pressure with a narrow pipe still gives poor flow.
Why it matters
- Combi boilers and unvented hot water cylinders work from mains water. They generally want at least 1 bar and a good flow, often 10 to 12 litres a minute or more for a combi.
- Showers and taps feel weak with low pressure or flow.
- Very high pressure, above about 5 bar, can stress fittings and appliances and cause noise or leaks. A pressure-reducing valve fixes that.
How to test it
- Pressure. A simple pressure gauge screws onto an outside tap. Check it when nothing else is running, and again at busy times in the morning and evening.
- Flow. Time how long it takes to fill a bucket of known size at your kitchen tap and work out litres per minute.
Test at different times, because pressure often drops when your neighbours are using water.
Common causes of low pressure
- A partly closed stopcock or isolating valve. Check they are fully open.
- A blocked filter or strainer on an appliance or valve.
- Old, narrow or partly blocked pipes, including old lead or galvanised pipes, which should be replaced.
- Leaks. A leak on your side of the meter lowers pressure.
- A shared supply, where several houses use one pipe.
- A problem with the network. If the pressure is low at the boundary stopcock, contact your water company.
Fixes
- Check valves and strainers.
- Replace old or undersized supply pipe, often to a larger bore.
- Fit a booster pump where the supply cannot be improved.
- Fix any leaks.
- If the problem is outside the property, report it to your water company.
We provide mains pressure upgrades and diagnose supply problems as part of our plumbing services. If you are thinking about a combi boiler, our combi boiler guide explains why supply matters. Contact us and we will test and advise.
