DIY GUIDE · PLUMBING & HEATING · CHECKED OCTOBER 2026
How to find a hidden water leak yourself
An evening. €4–€74 if you buy a vent key, a damp meter and a pressure test gauge.
Rule things out in order: toilets and taps, the attic tank, the meter test, the heating pressure. Find which part loses water before anyone lifts a floor.
- Every step, start to finish
- Checked October 2026 — sources at the end
- Honest about when to call a pro
FIRST, THE HONEST ANSWER
Do it yourself, or get a plumber?
Do it yourself if…
- You can reach your inside stop valve and close it, and you know where your water meter is if you have one
- You can get safely into the attic to see the cold tank
- The leak is slow — a damp patch, a rising meter or falling heating pressure — not water pouring through
- You are trying to narrow it down, not to cut into walls or floors
Get a pro if…
- Water is pouring or dripping through a ceiling now, or near the electrics
- The checks point to a leak under a solid floor, inside a wall or under the garden
- The sealed heating system loses pressure fast or the pressure relief pipe outside keeps discharging
- You cannot close the stop valve, or there is no inside stop valve at all
Safety first
- Water and electricity: if a leak is near lights, sockets or the board, switch off at the board from a dry place and do not touch wet fittings. Safe Electric advises that a safety switch tripping for no clear reason should be checked by a Registered Electrical Contractor.
- A ceiling holding water can come down suddenly. Keep people out from under it and put a bucket in place; do not push on it.
- In the attic, stand only on boards or joists. The HSA's ladder guidance asks for three points of contact and warns against the top steps of a stepladder; the same care applies getting through the hatch.
- Old attics can hold insulation fibre and, in older homes, materials that should not be disturbed. Wear gloves and a dust mask and do not break or cut anything up there.
- Never put your hand into a meter box in the footpath that you cannot see into, and do not force a stuck lid.
Stop here: Stop here: lifting floors, digging, the public side and gas
Opening floors and walls, and digging up an external supply pipe, need a plumber. Under Irish law the owner is responsible for leaks inside the house, as the CRU explains, while a leak on the external supply pipe between the boundary and the house can be investigated and repaired under Uisce Éireann's First Fix Free scheme, and anything at or beyond the meter is on the public side. If the falling pressure is on a gas boiler, any work on it is restricted to a Registered Gas Installer. If water has reached the wiring, the electrical side is for a Registered Electrical Contractor. How to hire a leak detection specialist →
| MATERIAL | COVERAGE | FOR THIS JOB |
|---|---|---|
| Toilet paper | A strip on the back of the bowl to test for a silent cistern leak | One per toilet |
| Masking tape and a pen | To mark damp patch edges and the time, so you can see if they grow | One roll |
| Food colouring | A few drops in a cistern; if colour reaches the bowl without a flush, the flush valve leaks | A small bottle |
How fast are you losing water
Flow = (second meter reading − first reading) ÷ hours between. If the meter moves 0.012 m³ in an hour with everything off, that is 12 litres an hour, or about 290 litres a day.
A cubic metre on the meter is a thousand litres. Write the readings down with the time, and do the test when nobody needs water.
The commonest hidden leak in an Irish home is a cistern trickling into the bowl or the overflow. The CRU's leak advice suggests listening for a constant sound of water and putting a strip of toilet paper on the back of the bowl: if it soaks with nobody using the toilet, water is getting past.
Most homes still have a storage tank in the attic that refills through a float valve. If you hear it refilling when nothing has been used, or see water from its overflow pipe on the outside wall, the valve is not shutting off or something it feeds is leaking.
A drip at a single tap can waste over 1,500 litres in a year. Check every tap, including the outside garden tap, which freezes in winter and splits quietly behind the wall.
If you have a meter, Uisce Éireann's meter test shows whether water is still flowing in with everything off. A leak between the boundary and the house is on the external supply pipe, which the First Fix Free scheme covers.
If your boiler has a pressure gauge, the system is sealed and should hold its pressure. One oil boiler maker gives a normal cold pressure of 0.5 and 1.0 bar for its sealed systems. If you top it up often, water is going somewhere: a radiator valve, a joint under the floor, or the boiler's own relief valve.
THE PART THAT DECIDES THE FINISH
Before you start — what kind of leak sign you have
Start from what made you suspect a leak. Each sign has its own first checks.
A damp patch on a ceiling
A brown ring or a soft area under a bathroom, the hot press or the attic tank.
- Mark the edge of the patch with masking tape and the date
- Look at what is directly above: a bath, a shower tray, a toilet or a pipe run
- Check whether it grows after the shower is used or all the time
- Keep everyone and any electrical fitting away from a sagging ceiling
A meter or bill that suggests constant use
A letter about a possible leak, or a meter that moves when nothing runs.
- Find the inside stop valve and make sure it turns
- Find the meter, usually in a boundary box in the footpath, and note how to read it
- Plan the meter test for a time when nobody needs water for an hour
- Check every toilet and tap first, so the test is not fooled by a cistern
A tank that keeps refilling
You hear water running into the attic tank at night.
- Plan a safe trip into the attic with a torch and good footing on the joists
- Look at the overflow pipe outside for drips first
- Listen at each toilet and the hot press to see what is drawing water
- Have a way to close the tank outlet valve if one is fitted
Heating pressure that keeps falling
A gauge on the boiler or near the hot press that drops below its usual reading.
- Note the pressure when cold, at the same time each day
- Look at the relief pipe outside, usually a short copper pipe near the boiler, for drips or a wet wall
- Check every radiator valve and the bleed screws for crusting or damp
- Find your boiler's user manual for its normal pressure
THE JOB
How to track the leak down
Set up and make it safe
15 minIf water is reaching any light, socket or the board, switch off at the board from a dry place and leave it off. Put a bucket under any drip. Mark any damp patch with tape. Gather a torch, notebook and stepladder, and tell the house you need an hour with no water used.
- Write the date and time next to each mark
- Photograph each damp patch to compare later
- Never stand under a sagging ceiling
Mistake to avoid: Poking a bulging ceiling to see how wet it is. Plasterboard full of water can drop in one piece.
Do the prep for your sign
15 minThis is the prep from the cards above. Find and test the stop valve, find the meter, note the heating pressure, or check the outside overflow. You want a starting point and a reading for each part you will test.
- Turn the stop valve closed and open again once, so you know it works
- Lift the meter box lid only if it opens easily; do not force it
- Look up at the outside walls for any overflow dripping
Mistake to avoid: Starting the meter test before you know the stop valve closes. You cannot tell an open valve from a leaking pipe.
Check the toilets
20 minLift each cistern lid and watch. Water running into the overflow means the fill valve is not shutting off. Then lay a strip of toilet paper on the back of each bowl and leave it for half an hour. If it soaks, or if food colouring added to the cistern turns up in the bowl, the flush valve is leaking.
- Do not flush during the test
- Mark which toilet you tested
- A slow refill noise from a cistern at night is a giveaway
Mistake to avoid: Skipping the toilets and going straight to the meter. A running cistern makes the meter move and sends you hunting for a pipe that is fine.
Check the taps and the outside tap
15 minLook at every tap for drips, including the outside garden tap. Feel the wall behind the outside tap for damp. Turn each tap on and off firmly and watch for water round the handle or spout base.
- Dry each spout with a cloth first, then watch
- Check under every sink with a torch for damp or crust on the joints
- Look behind the washing machine at its valve
Mistake to avoid: Ignoring the outside tap. A frost-split pipe behind the wall can leak into the cavity for months.
Check the attic tank
20 minClimb into the attic with care and look at the tank. Is the level steady, or rising to the overflow? Is the float valve shutting off? Look at the pipes leaving the tank and the floor round it for damp. Listen: if it refills and nothing downstairs has been used, something is drawing water.
- Stand only on boards or joists, never on the ceiling between them
- Keep three points of contact on the ladder going up and down
- Take a torch with a strap, so both hands are free
Mistake to avoid: Stepping off the joists to reach the tank. Your foot goes through the ceiling below, and a small leak becomes a big repair.
Run the meter test
70 minWith all toilets and taps checked and nothing using water, close the inside stop valve. Read the meter and write it down with the time. Uisce Éireann's guidance is to wait an hour and read it again. If the meter has moved with the stop valve closed, water is leaving between the meter and the house: the external supply pipe.
- Read every digit, including the red dials if you can see them
- Switch off any appliance that fills automatically, such as a water softener
- Repeat the test once to be sure
Mistake to avoid: Testing with the stop valve open. The reading then includes everything in the house, and tells you nothing about the pipe outside.
Test the heating pressure
20 minIf your boiler shows a pressure gauge, read it with the heating cold and write it down. Compare it with the normal pressure in your boiler's user manual; one maker gives 0.5 and 1.0 bar for its sealed systems. Check it again at the same time the next day. A drop with no bleeding in between means water is leaving the sealed circuit.
- Look at the relief pipe outside for drips after the heating has run
- Check every radiator valve and the pipes below them with dry kitchen paper
- Do not top up while you are measuring the drop
Mistake to avoid: Topping up every morning and calling it fixed. A sealed system that needs regular topping up is leaking, and fresh water brings in air and corrosion.
Follow the damp to its source
30 minFor a damp patch, use a damp meter on the plaster in a grid and mark the readings. Water runs along joists and pipes before it shows, so the wettest point is often not the centre of the stain. Work from the wettest reading towards whatever is above it: a bath seal, a shower tray, a toilet joint or a pipe.
- Run a shower or bath on its own and see if the patch grows
- Check the sealant round the bath and shower before blaming pipes
- Note readings on the tape so you can compare tomorrow
Mistake to avoid: Assuming the leak is directly above the stain. Water travels, and the first board you lift is often the wrong one.
Write it up and decide
15 minPut your findings in one list: which tests passed, which failed, the readings and times. A visible joint or a running cistern you can fix. A meter test that fails points to the external supply pipe. A falling heating pressure or a damp patch you cannot trace needs a plumber with that list.
- Give the plumber your readings; it saves them time and you money
- If the meter test fails, contact Uisce Éireann about the First Fix Free scheme
- Keep the marks on the ceiling until the leak is fixed
Mistake to avoid: Calling someone with no notes. Without your readings, they start the hunt from scratch, and you pay for it.
The mistakes that show
- Doing the meter test without first checking the toilets and taps
- Running the meter test with the stop valve open
- Topping up a sealed heating system every day instead of finding the leak
- Lifting floorboards directly under the stain without tracing the damp
- Stepping between joists in the attic
Stop here and get a plumber
- Your checks point to a leak under a solid floor, inside a wall or under the ground
- The sealed heating system loses pressure every day, or the relief pipe keeps discharging
- Water is coming through a ceiling near light fittings
- The stop valve will not close or there is no inside stop valve
| WHAT YOU SEE | WHY, AND THE FIX |
|---|---|
| Meter moves with the stop valve closed | Water is leaving between the meter and the house. That is the external supply pipe; contact Uisce Éireann about a First Fix Free investigation. |
| Meter still with the stop valve closed, but moves with it open and nothing running | The leak is inside the house. Recheck toilets, tanks and taps, then look for damp below pipe runs. |
| Attic tank refills all night | A float valve not shutting off, a running toilet or a leak on a pipe fed from the tank. Check the overflow and each cistern. |
| Water from the overflow pipe outside | The tank or a cistern float valve is set too high or worn. Lower the level or change the valve washer. |
| Heating pressure falls every day | Water is leaving the sealed system. Check radiator valves, the relief pipe outside and the boiler; get the expansion vessel checked at the service. |
| Damp patch only grows after showers | The shower tray seal, the waste joint or the sealant round the tray. Reseal or have the tray waste checked. |
| Damp at the base of an outside wall | A leaking outside tap pipe, a gutter overflowing, or ground water. Check the tap first, then the gutters after rain. |
| The safety switch trips after water use | Water may be reaching wiring. Leave it off and have a Registered Electrical Contractor check the installation. |
WHAT YOU SAVE
What it costs to do it yourself
| Radiator vent key | €3.79 |
|---|---|
| Damp and moisture meter | €40.95 |
| Water pressure test gauge | €29.49 |
| Total | €4–€74 |
| DIY total | €4–€74 |
Guide prices compiled by the Locufy team from published Irish and UK provider price lists and 2026/27 cost guides. Updated 2026.
The basic checks cost nothing. A damp meter and a pressure gauge are worth having if you have had one leak; a survey that finds the same thing costs many times more.
RATHER NOT?
Leak detection specialists near you, with prices shown
The ones who cover your area, nearest first, with one score from every review. No account needed to look.
Or post the job free and let them come to you.
Once the leak is fixed, read the meter on the same day each month. A sudden jump tells you something is wrong long before a ceiling stain does.
Let a damp ceiling or wall dry fully, checking with the damp meter, before you paint. Stain-blocking primer stops the brown ring showing through.
Wet ceiling board and plaster are construction waste and cannot go in household bins; mywaste.ie shows which civic amenity site near you takes plasterboard. Wet insulation should be bagged and taken the same way.
File the readings and what was found and fixed. If the leak returns, you or the plumber start from the answer, not from scratch.
Finding a hidden water leak: questions people ask
Check every toilet and tap first, then the attic tank, then do the meter test with the stop valve closed for an hour. If your heating has a pressure gauge, see whether it drops from one day to the next.
With everything off and the inside stop valve closed, read the meter, wait an hour and read it again, as Uisce Éireann describes. If it has moved, water is leaving between the meter and the house.
A leak on the external supply pipe between your boundary and the house can be investigated and repaired under Uisce Éireann's First Fix Free scheme. Leaks inside the house are the owner's responsibility.
A sealed heating system should hold its pressure. If it drops, water is leaving through a radiator valve, a hidden joint, the boiler's relief valve or a failing expansion vessel. Have a plumber or the boiler engineer check it.
It means a float valve is not shutting off, usually the attic tank or a toilet. It wastes water and can freeze and block in winter; lower the level or change the valve washer.
Locufy's Irish price guide puts leak detection at €150–€700 per survey, typically €350. Doing the basic checks first narrows the search and often the bill.
MORE GUIDES
More DIY guides
Sources — checked October 2026
- Grant — Vortex boiler user instructions: sealed system pressure, topping up, expansion vessel
- HSA — using ladders safely information sheet
- Uisce Éireann — check for leaks: the meter test
- Uisce Éireann — First Fix Free leak repairs and the supply layout
- CRU — water leaks in the home and the First Fix Free scheme
- Safe Electric — home safety: RCDs and when to call a Registered Electrical Contractor
- MyWaste.ie — plasterboard
- Ganly's — damp and moisture meter (price check)
- Woodie's — plumbing tools and accessories (price check)