Low Water Pressure in Your House: Causes and Fixes

A sudden drop in pressure usually means something has changed on your supply, not that your pipework has quietly worn out overnight — the most common causes are a stopcock or isolation valve that's been left part-closed, an airlock introduced after nearby plumbing work, or a fault on the mains outside the property.

• A stopcock or isolation valve not fully open
• An airlock trapped in the pipework, often after a repair nearby
• A mains-side fault or maintenance work from Thames Water
• Limescale build-up inside old pipes or a tap/shower head
• A boiler running below its correct pressure (combi systems)
• A hidden leak reducing pressure elsewhere in the system

If only one tap or shower is weak, the fault is almost always local to that fixture — think a clogged shower head, a kinked hose, or a part-closed valve behind that outlet — rather than a problem with your incoming supply. If every tap in the house is weak, including outside taps, the cause sits further upstream: your stopcock, an airlock, or the mains itself.

Testing this takes two minutes and points you straight at the right fix, which is why it's the first thing we ask about on the phone before sending anyone out.

London's older housing stock and variable mains network mean low pressure shows up more often here than in newer-build areas — particularly in period conversions, upper-floor flats, and streets on higher ground across Tower Hamlets, Hackney, Islington and Southwark. Ageing internal pipework, undersized risers in converted Victorian terraces, and shared supplies in multi-let buildings all make pressure loss more likely than in a modern estate with wider modern pipe runs.

That doesn't mean every low-pressure complaint in East London is a lost cause — most turn out to be a fixable internal issue rather than something Thames Water needs to resolve.

Yes — on a combi boiler, your hot water pressure comes directly from the boiler's own sealed system, so a low reading on the boiler's pressure gauge shows up as weak hot taps and showers throughout the house, even while cold pressure stays normal. On an older gravity-fed system with a cold water tank in the loft, pressure instead depends on how high that tank sits above the outlet, the condition of the ballcock valve, and whether air has got into the feed from the tank — a different set of checks entirely.

Knowing which system you've got tells you where to look first: the boiler casing for a combi, or the loft tank and its feed pipe for a gravity-fed setup.

Yes — an airlock is one of the most common causes of sudden, patchy low pressure, and it happens when a pocket of air gets trapped in a pipe run, most often after work on nearby pipework, a drained system, or a burst that's since been repaired. It typically shows up as spluttering, banging, or a tap that runs weakly for a moment before picking up, rather than a steady weak flow.

Clearing one is usually straightforward: run the affected tap fully open, then briefly open and close a nearby outlet or the stopcock to push a burst of water pressure through the line and dislodge the trapped air — repeat at a couple of different taps if the first attempt doesn't shift it. If the spluttering comes with knocking or banging from the pipework itself, see our guide to noisy and banging pipes.

Not directly, but a stuck or part-closed radiator valve can drop pressure on your central heating loop, which shows up as a low reading on the boiler gauge and, in turn, weaker hot water on a combi system. It's also common on older systems for a lockshield valve to have been left slightly closed after bleeding a radiator, which restricts flow through that circuit without anyone noticing until the boiler pressure starts dropping.

If your heating pressure keeps falling and you've recently bled a radiator, check that both valves on it are back to their original position before assuming there's a leak.

Work through these checks in order — most low-pressure complaints are resolved by step three, and the rest tell you clearly whether the fault is inside your home or on the mains.

1. Check whether it's one tap or the whole house. Turn on a tap you don't normally use, then check the kitchen, bathroom and any outside tap. If only one outlet is weak, the fault is local to that fixture (head, hose, valve); if everything is weak, it's a supply-side or airlock issue.
2. Check your stopcock and any isolation valves are fully open. Find your internal stopcock (usually under the kitchen sink or near the front door) and turn it fully anticlockwise. Do the same for any isolation valves under sinks, behind toilets, or feeding a shower — these are often left part-closed after previous work.
3. Bleed the affected tap or pipe to clear an airlock. Turn the affected tap fully on, then briefly open and close a nearby tap or the stopcock to send a burst of pressure through the pipe — this often dislodges a trapped air pocket. Repeat at a few outlets if the first attempt doesn't clear it.
4. Check the boiler pressure gauge (combi systems). Look at the pressure gauge on the boiler itself — it should typically sit in the manufacturer's marked green zone. If it's reading low, you can usually top it up yourself using the boiler's filling loop, following the instructions on the boiler casing or manual.
5. Ask a neighbour if they've lost pressure too. If the whole street or building has lost pressure at the same time, it's almost certainly a Thames Water mains issue rather than anything in your own pipework, and no amount of internal fixing will resolve it — check thameswater.co.uk or wait for it to clear.
6. Call a plumber if none of the above fixes it. If pressure is still low after checking valves, clearing airlocks and confirming boiler pressure, the cause is likely a hidden blockage, a failing valve, or a case for a booster pump — at that point it needs a proper diagnosis on site.

Call a plumber once you've ruled out a closed valve, an airlock and a mains-side fault and the pressure is still low — at that point the cause is usually a hidden blockage, a failing valve, or a system that genuinely needs a booster pump, and none of those are worth guessing at. It's also worth calling straight away if low pressure appeared alongside a damp patch, a running water meter, or a noise in the walls, since that can point to a leak rather than a simple airlock.

If the issue is specifically at your shower, our shower repair page covers pump, valve and cartridge faults in more detail. If you've got no water at all rather than just low pressure, or the pressure loss came with a leak, treat it as urgent and see our emergency plumber page — we cover Tower Hamlets, Hackney, Islington, Newham, Southwark and the wider London area from our E1 base.

It depends entirely on the cause — clearing an airlock or adjusting a valve is a quick visit, while diagnosing a hidden fault or fitting a booster pump is a bigger job, so we won't quote a figure without seeing the system first. Every visit comes with a free, no-obligation quote, so calling to ask costs you nothing. For more detail on how we price jobs, see our pricing page.

Need this fixed by someone local? See our page for a plumber in Tower Hamlets for borough-specific coverage and response times.