Low water pressure: what causes it and how to fix it
Low pressure at a single outlet is nearly always a blocked aerator, a scaled cartridge or a partly closed isolation valve. Low pressure everywhere points at the incoming supply: a partly closed stop tap, a failing pressure-reducing valve, a blocked filter, or a shared supply pipe that cannot deliver enough flow.
Key facts
- One tap only
- Blocked aerator, scaled cartridge or a part-closed isolation valve
- Whole property
- Incoming supply, stop tap not fully open, or a shared supply issue
- Hot only
- Scaled cylinder, coil or a failing shower valve
- Attendance
- £99 in standard hours including the first hour
Symptom to likely cause
| Symptom | Most likely cause |
|---|---|
| Poor flow at one outlet | Aerator scaled up, cartridge failing, or the isolation valve under the basin is part closed. |
| Poor flow everywhere, hot and cold | Incoming main restricted, stop tap not fully open, or low mains pressure locally. |
| Poor hot flow only | Scale in the cylinder coil, a failing shower valve, or a gravity system with little head. |
| Pressure drops when another tap runs | Undersized supply pipework, common in converted flats. |
One tap or the whole house?
Test every cold tap in the property, then every hot one. The pattern tells you where to look.
- • One outlet only — aerator, cartridge, flexible tail or isolation valve at that fitting.
- • All hot outlets weak, cold fine — a cylinder, coil or hot-side scale problem rather than the mains.
- • Everything weak — the incoming supply, stop tap, pressure-reducing valve or filter.
- • Weak only when other outlets run — the supply pipe or system cannot deliver enough simultaneous flow.
Things worth checking before you call
All of these are safe to do yourself.
- • Make sure the internal stop tap is fully open — they are often left part-closed after earlier work.
- • Unscrew and rinse the aerator on the affected tap; limescale grit blocks them routinely in hard water areas.
- • Check whether neighbours have the same problem, which points at the street main rather than your property.
- • Check any whole-house filter or softener bypass, if one is fitted.
What a plumber can actually change
Some causes are fixable in an hour: descaling or replacing cartridges and aerators, freeing or replacing a seized stop tap, replacing a failed pressure-reducing valve, or clearing a blocked filter. Others are structural — an undersized or shared supply pipe, or genuinely low mains pressure in the street — and the honest answer there is a pump, an accumulator or a supply upgrade rather than a quick repair.
We will tell you which category you are in before you spend money on the wrong fix.
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