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No drip, no puddle, no obvious cause — yet the bill is up, the pressure keeps sliding, or a patch is spreading on the wall. Here's how to be sure.
How do I know if I've got a hidden leak? Turn off every tap and appliance, then watch the water meter for ten minutes — if it's still counting with nothing running in the house, water is escaping somewhere unseen. A damp patch that keeps growing, a boiler that needs repeated topping up, or an unexplained rise in the water bill are the other three signs worth taking seriously. If the test confirms it, ring 020 4577 2888 and describe what you've found.
Everything off, then watch the meter for ten minutes. If it's still counting, water is going somewhere it shouldn't.
Turn off every tap in the house, make sure no appliance is mid-cycle, and if you have an outside tap, check that too. Find your water meter — often near the boundary under a small cover, or in a utility room on newer builds — and either read the digits and check again after ten still minutes, or watch the small triangular or star-shaped leak indicator that spins on most modern meters even at a trickle of flow.
If the digits have moved, or the indicator is turning, with absolutely nothing running inside or outside the house, that's about as close to proof of a hidden leak as a householder can get without lifting a floorboard. It doesn't yet tell you where the leak is — only that one exists — which is exactly the information worth having ready when you ring.
A patch that grows steadily, smells of damp rather than must, and sits near a known pipe run is the pattern worth acting on. Not every stain is plumbing.
Condensation, a slipped roof slate, blocked guttering overflowing down an outside wall and rising damp in an older solid wall can all leave marks that resemble a pipe leak at a glance — which matters, because chasing a plumber for a roofing fault wastes everyone's time. The clues that lean toward plumbing: the stain sits below or beside a bathroom, kitchen or airing cupboard rather than an outside wall exposed to weather; it keeps darkening and spreading over days rather than only appearing after heavy rain; and it carries a persistent damp smell rather than the mustier scent of trapped condensation.
In the Victorian terraces near the town centre and harbour, old cast pipework and stacks patched in stages over a century make a hidden leak more likely to be plumbing than in a newer build — worth bearing in mind when weighing up the cause. Either way, the meter test in Notice 1 settles the question faster than staring at the ceiling.
A sealed heating system that needs the filling loop again within days is very often losing water into a hidden leak, not just "settling."
Central heating runs as a closed loop, so if the pressure gauge keeps sliding despite regular top-ups, the water has to be escaping somewhere — commonly a weeping radiator valve, a joint under a floor, or a pinhole in a pipe run buried in a wall. Every top-up through the filling loop is, in effect, refilling the same leak rather than solving anything, which is why this pattern deserves an engineer's look rather than an ever-growing habit of topping up.
If your boiler pressure and your water meter are both misbehaving at once, that's a strong signal the two issues are the same leak, and it's worth mentioning both when you ring — it narrows down where a plumber starts looking considerably.
A leak nobody can see keeps running for weeks, quietly rotting timber and growing mould the whole time — that's what makes it worth chasing early.
A dripping tap is a nuisance that gets fixed because it's impossible to ignore. A pipe leaking gently under a solid floor, inside a stud wall, or beneath floorboards can run for months announcing itself only through a subtle smell, a slightly warm patch of floor over a hot water pipe, or a water bill that's crept up without explanation. By the time it becomes visible as a stain or a bulge, joists, plaster and skirting may already be affected.
This is the practical case for running the meter test the moment something feels off, rather than waiting for a visible sign — an unexplained bill, a boiler that won't hold pressure, a faint musty smell in one room. Catching it at that stage is a plumbing job; catching it after months is a plumbing job plus a building repair.
A leak that persists even with your own stopcock fully closed, or water surfacing outside your boundary, points at the supply pipe or the public main — NI Water's territory, not yours.
Before assuming a hidden leak is entirely your own cost to bear, close the internal stopcock fully and watch the meter again. If it stops counting, the leak sits somewhere inside your own pipework, from the stopcock inward, and is your responsibility to have repaired. If it carries on regardless, the leak is likely in the supply pipe between the boundary and the meter, or in the public main itself — and in Northern Ireland that side of the boundary is generally NI Water's to fix.
A soft, unexplained wet patch on a footpath, verge or garden well away from the house, especially one that never quite dries even in settled weather, is worth reporting to NI Water directly rather than paying a plumber to investigate ground that isn't theirs to open. When in doubt, a plumber can help establish which side of the boundary the leak sits on before any digging starts.
Turn off every tap and appliance in the house, then either watch the digits on your water meter for ten minutes with nothing running, or note the position of the small triangular or star-shaped leak indicator on the meter dial. If the meter is still counting, or the indicator is still spinning, with every fixture in the house switched off, water is going somewhere it shouldn't be — which points at a hidden leak in the pipework rather than a visible drip you simply haven't found yet.
No. Condensation, a failed roof slate, blocked guttering or rising damp in an older wall can all mimic a pipe leak's staining. The clues that point toward plumbing are a patch near a known pipe run, a patch that grows steadily rather than only appearing in cold or wet weather, and a smell of damp rather than simple mustiness. When in doubt, the stopcock and meter test settles which kind of problem you're dealing with.
Because a visible drip announces itself and gets fixed quickly, while a hidden leak inside a wall or under a floor can run for weeks or months unnoticed, quietly rotting timber, growing mould and undermining plaster the whole time. By the time it shows as a stain or a smell, real damage may already have been done, which is why the meter test is worth running the moment pressure or bills start behaving oddly, not just when something becomes visible.
It's possible, and worth ruling out before assuming the cost is yours. Water pooling on a footpath or verge outside your boundary, or a leak that carries on even with your own stopcock fully closed, points at the supply pipe or the public main rather than your internal pipework — and that side is generally NI Water's to fix, not a private plumber's.
The main notice — how the line works and the waters it covers.
Go to home →Close the stopcock before all else — the full standing orders.
Read the notice →Pressure, error codes, oil and gas — and the gas standing order.
Read the notice →What to attempt, and when it's NI Water's sewer instead.
Read the notice →How charging works and the questions to put before work starts.
Read the notice →Pressure, controls, the immersion — checks in order.
Read the notice →Gentle thawing from the tap end, and never with a flame.
Read the notice →Meter watched, patch inspected, boundary test run? If the leak is yours to fix, ring any hour and describe what the test showed to a local plumber covering Carrickfergus and the villages around it.
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