What A Thames Water Constant‑Flow Alert Really Means
A constant‑flow alert is raised when your smart meter records uninterrupted water use for several hours, often overnight. Thames Water typically sets thresholds to catch steady, low flows that don’t match normal household patterns. It’s a red flag for leakage rather than a one‑off long shower.
Common benign causes include a running toilet, a stuck ballcock in a cold‑water tank, an outside tap left on, irrigation, or a water softener regenerating. Hidden pipe leaks are also common. Act quickly but don’t panic. Begin systematic checks within 24 hours to limit damage and costs. If water is already spreading, follow our rapid safety steps in the emergency water leak guide.
Rapid Triage (10 Minutes): Rule Out Normal Use
First, pause obvious users. Turn off dishwashers, washing machines, garden irrigation and any softener regeneration cycle. Make sure taps are fully shut and hose guns aren’t dribbling. Check toilets; a faint trickle or hiss suggests a running cistern.
Open your Thames Water app or look at the meter’s flow indicator. Note the time and current flow reading. If the flow persists with everything off, you likely have a leak. Move to isolation tests. For a step‑by‑step plan to contain damage and shorten diagnosis, see how to track a leak and reduce damage fast.
Confirm A True Leak With Stop Tap And Meter Tests
Find both stop taps: the internal stop tap (often under the kitchen sink or in a utility cupboard) and the external stop tap in the boundary box. Ensure no one uses water while testing.
Test A (15 minutes): with all use off, watch the meter’s flow indicator. Any continuous movement suggests a leak. Test B (street vs internal): fully close the internal stop tap; if the meter still moves, suspect a service pipe leak between street and house. Test C (overnight): record the meter last thing and again at dawn to catch small leaks. For service‑pipe responsibility, read street to stop tap: who pays. Slow, intermittent loss is covered in what is a slow water leak.
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Separate Mains Water Leaks From Central Heating Leaks
If your combi or system boiler keeps losing pressure and you’re topping up often, you may have a heating circuit leak. That won’t show on the water meter once the filling loop is closed. Safely isolate the filling loop and monitor boiler pressure for at least a few hours.
If you have zone valves, isolate upstairs/downstairs or individual zones to narrow the issue. Never leave the filling loop open. If you’re unsure, stop and call a professional. Learn more about targeted testing at central heating leak detection.
Isolate Internal Zones Room‑By‑Room
Start with toilets. Add food colouring to the cistern; if the colour seeps into the bowl without flushing, replace the fill/flush valves. Turn off each toilet’s isolation valve and check the meter; if flow stops, you’ve found the culprit. Repeat for each WC.
Isolate appliances using their service valves (washers, dishwashers, softeners) and retest the meter after each change. If you see marks on ceilings or feel damp floors, protect electrics, contain drips with a bucket, and prioritise that branch. Keep notes of what you turned off and when; this record speeds up diagnosis by Track A Leak or your plumber.
Check The Service Pipe And Outside Areas
Close the external stop tap in the boundary box. If the meter continues to move, report it to the water company. With the internal stop tap open and no internal use, listen at the boundary box and internal stop tap for hissing or vibration, which often indicates a buried leak.
Walk the front path, drive and garden. Look for unexplained damp patches, puddles after dry spells, or lush growth lines. In flats or shared supplies, ask the managing agent to coordinate riser access and timed shut‑offs for neighbouring flats. If you suspect a supply‑pipe fault, see water mains leak detection specialists.
Decide: Continue DIY Monitoring Or Call A Professional
Book professional leak detection if the meter shows constant flow after basic isolations, if you suspect a buried or service pipe leak, if boiler pressure drops with the filling loop shut, or if access and safety prevent testing. Track A Leak pinpoints leaks with acoustic listening, thermal imaging, tracer gas and endoscopy, keeping disruption low.
Prepare for a visit: screenshots of your meter or app, notes from each isolation step, any known pipe routes, and clear access to stop taps and risers. This cuts time on site and speeds the fix.
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Insurance And Thames Water Support
Call your insurer to confirm Trace & Access cover for finding the leak and any related damage. Keep a log of meter readings, photos and short videos of damp, and a timeline of what you isolated and when. This evidence supports claims and reduces queries.
If you confirm a supply‑pipe leak, report it to Thames Water and ask about leak allowances after repair. Keep written reports and invoices from Track A Leak or any contractor. They help with both insurance and any water‑bill adjustments.
After The Fix: Prevention And Monitoring
Re‑enable smart alerts in your Thames Water app and set low‑flow notifications. Log monthly readings and check night‑time graphs for flat‑line zero flow. A quick glance each week can save hundreds of pounds and avoid damage.
Add or service isolation valves for bathrooms, appliances and outside taps so you can test zones quickly next time. Periodically check toilets, overflow pipes and visible joints. A two‑minute check during routine cleaning is often enough to catch issues before they escalate.
London Specifics: Flats, Permits And Practicalities
In flats, coordinate with the managing agent to access risers, corridor valves and plant rooms. Label which flats are isolated and record timings so you can compare meter behaviour. Agree a call tree for re‑pressurising and reinstating services.
If a pavement excavation is needed, expect council permits and traffic management. Plan for parking restrictions, concierge or fob access, and lift bookings in busy blocks. Clear, scheduled access helps Track A Leak complete testing and repairs in a single visit.
Get Help Now: Book Leak Detection In London
If your meter still shows constant flow or you see fresh damage, book a diagnostic survey. Track A Leak covers bathroom and ceiling leaks, central heating leaks, water mains tracing and non‑destructive leak detection across London and the Home Counties.
Call for rapid advice or request a same‑day visit where available. Share your notes, photos and meter screenshots when booking. Start now and get a quote.
FAQs
How do I find my stop tap?
Look under the kitchen sink, in a utility cupboard, or near the front door for the internal stop tap. The external stop tap sits in a boundary box on the pavement or drive.
Will Thames Water fix a leak on my property?
They usually fix leaks on their side of the boundary. Leaks on your supply pipe or inside are normally your responsibility, though some allowances may apply once repaired.
How much water can a running toilet waste?
Often hundreds of litres per day. Even a slow trickle can keep your meter in constant‑flow and inflate bills.
What if I can’t turn the external stop tap?
Do not force it. Try the internal stop tap to make the property safe and contact your water company or a professional for assistance.
Does a constant‑flow alert always mean a leak?
No. It can be caused by normal but continuous use, like irrigation or softener regeneration. A quick isolation test will confirm.
How soon should I call a professional?
Call if flow persists after basic checks, you suspect a buried leak, or boiler pressure keeps dropping. Early detection limits damage and reduces cost.
