Signs of a Hidden Water Leak

Most hidden leaks are found late, not because the signs were absent but because each one on its own had an innocent explanation. A higher bill was the new tariff; the damp patch was the weather; the boiler always needed topping up. Put two of them together and you almost certainly have a leak. This page lists the signs by system, the checks you can safely make yourself, and the point at which it is worth calling us.

Signs of a leak on the mains or supply pipe

• A water bill that has risen with no change in the household
• The meter turning, or its small leak indicator spinning, with every tap and appliance off
• Water pressure at the taps lower than it used to be, especially first thing in the morning
• The sound of running water in a wall, under a floor or at the stop tap when nothing is in use
• A wet patch, a lush green strip or sunken paving in the garden or drive along the line of the supply pipe
• Water standing in the meter chamber or around the outside stop tap

Signs of a central heating leak

• The boiler pressure gauge dropping over days or weeks and needing topping up
• The boiler locking out on low pressure, usually first thing in the morning
• A warm patch on a solid floor, or a line of warmth you can feel with a bare foot
• A radiator that never quite fills, or air that keeps returning to the same radiator
• Damp that appears when the heating is on and dries when it is off

Two other things mimic a heating leak and are cheaper to fix: a failed expansion vessel and a pressure relief valve that is discharging outside through its copper pipe. We test both before any floor is surveyed. The central heating page explains the sequence.

Signs of a hot water or underfloor heating leak

• A hot tap that takes longer than it did to run warm, or runs warm then cools
• One underfloor heating zone that no longer heats, or a manifold that needs regular topping up
• Warmth in a floor where there should be no pipe, or a floor that stays warm after the system is off
• Skirting boards swelling, laminate lifting or tiles sounding hollow in a line

Checks you can make yourself

1. The meter test. Find the meter, usually in a chamber near the boundary or under the kitchen sink. Turn off every tap and appliance, including the washing machine, dishwasher, water softener and any garden tap, and make sure no toilet is refilling. Note the reading, wait half an hour to an hour, and read it again. Any movement is water leaving the system somewhere.
2. Inside or outside. Close the internal stop tap and repeat the meter test. If the meter still moves, the leak is on the supply pipe between the meter and the house. If it stops, the leak is inside.
3. The boiler pressure test. Note the pressure on the gauge with the system cold. Do not top it up. Check again the next morning. A fall with no water at the pressure relief pipe outside points to the pipework; a wet pressure relief pipe points to the boiler or expansion vessel.
4. Toilets and overflows. A cistern that leaks past its flush valve into the pan is the most common cause of a moving meter. A few drops of food colouring in the cistern will show up in the pan within twenty minutes if the valve is passing. Look outside for dripping overflow pipes too.
5. Listen at night. With the house quiet, put an ear to the stop tap or the rising main. A steady hiss with everything off is a pressurised leak talking.

Please do not go further than this. Lifting floors, chasing walls or digging along a suspected pipe route on the strength of a damp patch is how properties get damaged in the wrong place, and it can affect an insurance claim. The survey process exists to put one small opening exactly where it is needed.

What is often not a leak

Condensation on cold surfaces, rain getting in around a window or a blocked gutter, rising damp in an old wall, and a washing machine hose that drips only on the spin cycle all produce damp that looks like a leak. A meter that stands still and a boiler that holds pressure are strong evidence that the water is coming from somewhere other than a pipe, and if that is what we find we say so. A tight-system result is a real finding, and the report explains it.

When to call

• The meter moves with everything off, whether or not you can see any water
• The boiler loses pressure with nothing at the relief pipe
• Damp keeps returning in the same place after it has been dried
• Water is causing damage now and you cannot find where it is coming from
• Your insurer or letting agent has asked for a leak detection report

Advice on the phone is free, and if the symptoms do not sound like a leak we will tell you on the call rather than book a survey. Typical costs are on the pricing page.

How a survey works

A survey runs in a fixed order. Pressure and flow tests prove which system is losing water and rule out the innocent ones. Pipe tracing maps where the pipes actually run. Thermal imaging, acoustic listening and tracer gas are then used as the evidence demands, and a leak is not called found until two methods agree. The location is marked and photographed, and you receive a written report the same week, formatted for a trace and access insurance claim if you need one.

While you wait for the survey

If water is damaging the property, turn it off at the stop tap and protect what you can. Otherwise leave the system live and do not drain the heating, because a pressurised leak is far easier to pinpoint than an empty pipe. Keep a note of meter readings and boiler pressures with dates, and take photographs of any damp as it appears; both are useful evidence for the report and for your insurer.