Plumbing
What Causes Low Water Pressure in a House?
Published 17 December 2025 by WDI Group (Surrey) Ltd
Low water pressure shows up in frustrating ways — a shower that dribbles rather than sprays, taps that take an age to fill a kettle, or a washing machine that struggles to fill properly. The cause can sit anywhere from the street main to a single blocked showerhead.
Working out whether the problem affects the whole house or just one fitting is the quickest way to narrow things down.
It also helps to note when the problem started. A sudden drop often points to a specific event, such as a valve being knocked shut, a new leak developing, or nearby works affecting the mains supply, while a gradual decline over months or years is more often about ageing pipework or scale build-up narrowing the bore of the pipe.
Whole-house low pressure
- A partially closed stopcock, sometimes left that way after previous work
- A problem with the incoming water supply, worth checking with your water company
- Scale build-up throughout ageing pipework restricting flow generally
- A shared supply pipe with other properties experiencing high demand
Low pressure at a single tap or shower
- A blocked aerator or showerhead clogged with limescale — usually solved by soaking in descaler
- A partially closed isolation valve under the sink
- A kink or restriction in a flexible supply hose
- A fault specific to that fitting rather than the wider system
Pressure that's dropped gradually over time
A gradual decline, rather than a sudden change, often points to limescale slowly narrowing pipework internally, particularly in hard water areas. This tends to affect older galvanised or copper pipework more than modern plastic systems.
Pressure that changes with demand elsewhere in the house
If pressure drops noticeably when another tap or appliance is running, this points to your incoming supply pipe or internal pipework being undersized for current demand, rather than a fault as such. This is common in older properties that have had bathrooms or appliances added since the original pipework was installed.
Combi boiler-related pressure issues
If low pressure specifically affects hot water while cold water pressure is fine, this points towards the boiler itself rather than the household supply — worth checking the boiler's own pressure gauge and looking into any restrictions on the hot water side.
Checking and topping up your boiler's system pressure
It's worth distinguishing between mains water pressure, which affects taps and showers fed directly from the supply, and a combi boiler's internal system pressure, which affects central heating and can cause radiators to heat poorly or the boiler to lock out with a fault code. Most combi boilers display their pressure gauge on the front, and the manufacturer's manual will show the correct range, usually around 1 to 1.5 bar when the system is cold.
- Locate the boiler's filling loop, usually a braided flexible hose with two valves
- With the boiler off, slowly open the filling loop valves until the gauge reaches the correct pressure
- Close the valves fully and check the pressure holds rather than dropping straight back down
- If pressure keeps dropping after topping up, this points to a leak somewhere in the system rather than simple air loss
What an engineer checks for a whole-house pressure complaint
When we're called out for low pressure, the first step is usually confirming whether it's a mains supply issue, an internal pipework issue, or a boiler issue, since each is diagnosed and resolved differently. This typically involves checking pressure at an outside tap close to the supply, checking the stopcock is fully open, and working through internal isolation valves before assuming a bigger job like pipework replacement is needed.
Need help with this in your own home?
Cheam Plumbing is part of WDI Group (Surrey) Ltd. Call 020 3727 2578 and we will advise on availability and the quickest response we can provide, or view our published rates before booking.