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A leak you can see is an errand. A leak you can't see is a slow demolition. Here's how to read the early signs — and the one test that settles whose pipework the trouble is on.
Suspect a hidden leak? Run the stopcock test tonight. Turn off every tap and appliance, close the stopcock, and watch — if a damp patch stops growing or a hiss goes quiet, the leak is on your own pipework. Water near electrics, or a ceiling starting to sag? That's now, not tonight: ring 020 4577 2888 any hour to be connected with a local plumber.
Damp patches, stains, a musty smell, a hiss in a quiet house, boiler pressure that keeps sliding. One sign is a suspicion; two together is a finding.
Hidden leaks announce themselves in dialect: a damp patch on a wall or ceiling that grows or never dries, a tide-mark stain on the ceiling below the bathroom, paint bubbling, a skirting board darkening, a musty smell that lives in one room only, floorboards lifting at their edges. Stand somewhere quiet late at night and listen — a faint, continuous hiss with every tap off is water going somewhere it shouldn't.
Two more tells. A boiler pressure gauge that keeps sagging is a leak on the heating circuit, even if you never see a drop — the card below explains. And if your home has a water meter (most houses in the north don't), usage climbing with no change in habits is the numerical version of the same story. In an older terrace, take a damp patch on a party wall seriously: where generations of pipework meet, the joints fail first — and rarely alone.
Everything off, stopcock closed, then watch and listen. The test won't find the leak — it tells you whose problem it is.
Turn off every tap and every water-using appliance. Close the stopcock — under the kitchen sink in most homes. Now observe. If the hiss stops, or a damp patch you've outlined in pencil stops advancing over the next few hours, the leak sits on your own pipework, downstream of the valve. If water keeps arriving with the stopcock shut, or wells up out of the ground outside, suspect the supply pipe or the main — the public side is NI Water's territory, and the burst pipes guide covers whose pipe is whose.
If your home does have a meter, add the precise version: read it, use no water at all for 30 to 60 minutes, and read it again. Movement on a closed system is a leak measured in numbers rather than suspicions. Either way, what you learn is worth a sentence on the phone — "it stops when the stopcock's closed" cuts diagnosis time before anyone arrives.
If it keeps happening, yes — somewhere on the heating circuit. Every top-up just feeds the leak fresh water to lose.
A sealed heating system holds its water, so a gauge that needs topping up week after week is telling you plainly that water is leaving. The usual suspects: a weeping radiator valve, a joint under a floor, occasionally the boiler's own internals. The unnerving part is that the leak can be small enough never to show as a visible drip while still soaking a joist, quietly, for months.
Do the free checks first — run a hand around the visible radiator valves and pipework feeling for damp, and look for the white crust that marks a slow weep. Then stop topping up and start booking: the water is going into the fabric of the house somewhere, and the boiler problems guide tells the full pressure story.
Water near electrics, a bulging or sagging ceiling, a patch spreading while you watch. Any one of those: stopcock off, then ring.
Most hidden leaks are slow, which buys you time to be methodical — mark the patch, run the test, make the call in daylight with your findings ready. Three signs cancel that luxury. Water anywhere near sockets, light fittings or the consumer unit is an electrical hazard wearing a plumbing costume. A ceiling that bulges or sags is holding water and choosing its moment — stay out from under it. And a damp patch visibly spreading is, by definition, no longer slow.
In any of those cases: stopcock closed, electricity off at the consumer unit if you can reach it dry-footed, and ring — any hour, that being the entire point of the line.
Run the stopcock test: turn off every tap and water-using appliance, close the stopcock, then watch and listen. If a hiss goes quiet or a pencil-marked damp patch stops advancing, the leak is on your own pipework. If your home has a water meter, add the precise version — read it, use no water for 30 to 60 minutes, read it again.
Most homes in Northern Ireland aren't metered, so a rising bill usually isn't the clue it would be elsewhere — here the leak announces itself through damp patches, stains, a musty smell or a hiss instead. If your home does have a water meter, unexplained climbing usage is worth taking seriously and checking with the meter test.
Because water travels. It follows joists, wall cavities and the backs of plasterboard, then surfaces at the lowest convenient point — so the stain marks where the water settles, not where it escapes. That's normal, worth mentioning on the phone, and a good reason not to cut holes on a guess.
If it keeps dropping, yes — a sealed heating system holds its water, so a gauge that needs topping up again and again means water is leaving the circuit somewhere, even if you never see a drip. Check the visible radiator valves for weeps and white crust, then stop topping up and get it looked at.
Three signs cancel the watch-and-wait: water anywhere near sockets, light fittings or the consumer unit; a ceiling that bulges or sags; and a damp patch you can see spreading. Any of those — stopcock off, electrics off if you can reach the consumer unit dry-footed, then ring straight away.
The main page — the triage board and the areas this line covers.
Go to home →The sixty-second triage for escaping water.
Read the guide →Pressure drops, no heat, error codes — and the gas rule.
Read the guide →Pressure, timer, tripped switch, diverter valve — the checks before the call.
Read the guide →Prevention that costs pennies, thawing that doesn't end in a flood.
Read the guide →What to try, what never to pour, and when it's NI Water's sewer.
Read the guide →No invented prices — how charging works and what to ask first.
Read the guide →Ring any hour to be connected with a local plumber covering Derry and the villages around it — and say what the stopcock test told you.
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