Loft Water Tank Leak Detection Across London
A loft survey checks the cold water tank, its float valve, the overflow and the pipework around them, then reads the ceilings below for moisture. The aim is to separate a wet joint from a passing valve or condensation before anyone cuts into plaster. The package is £580. No VAT is charged.
What the visit covers
- The tank body, lid, seams and every connection on its sides and base
- The float valve and the overflow or warning pipe, including where the overflow ends outside
- Cold feed, hot water expansion and distribution pipework in the roof space
- Moisture readings on the ceilings and walls below the tank and along the pipe runs
- A written report of what was found and where, with the limits of each reading
Published prices
What it costs
- Fixed-price leak location package
- The package gives one fixed price, known before the visit, to locate a leak in one property using whichever methods the leak needs.
- £580Fixed price
Or by the hour
- Standard leak detection
- General water leak detection in a property.
- £180an hour
No VAT is charged
A fixed hourly rate that cannot rise on the day
No find, no fee applies when a live leak inside your own property cannot be located. No find, no fee in full
Order of work
Read the signs from below
Ceiling stains, damp patches and the sound of running water give the first map. The wet area is measured with a moisture meter before anyone goes up, because a stain is rarely under its source.
Look from the hatch
The tank, valve and overflow are inspected from the hatch with a torch, and the loft is entered only where there are boards or a safe route along the joists. Condensation, a weeping joint and a passing valve each leave different marks.
Test the suspect
If the float valve may be passing, the tank level and the overflow are watched with the draw-off points quiet. If a pipe is suspected, it is isolated and tested by pressure, with thermal imaging or an endoscope where they help. The finding is marked and written up.
What a loft tank survey looks at
A loft cold water tank is a small system rather than one fitting. Water arrives through a float valve, sits in the tank, leaves through one or more pipes, and the overflow or warning pipe waits at the top to show when the valve has failed. Most loft water problems come from one of those four places, plus condensation on the tank and the pipes. In a traditional tank-fed system the same tank also feeds the hot water cylinder, so a wet airing cupboard below the loft is worth reading alongside it.
The Water Supply (Water Fittings) Regulations 1999 (Schedule 2, paragraph 16) expect the supply to a storage cistern to have an effective adjustable valve that shuts off the inflow below overflow level, and a servicing valve on the inlet next to it. The survey checks that each of those, and the overflow, is present and behaving, because a missing or seized part can explain a lot of loft water.
The tank itself is looked at last. Modern tanks are plastic and tend to fail at fittings rather than in the plastic. Older galvanised or lined tanks can corrode at seams and around old connections, which is covered in a cold water storage tank that is leaking.
Why the stain is rarely under the fault
Water in a loft runs along the top of the ceiling, follows a joist, and drops where the plasterboard is weakest or a ceiling light cut-out lets it through. A stain over the landing can come from a tank above the back bedroom. That is why the first reading is taken below and the second above.
Loft insulation adds to the problem. Mineral wool can hold a good deal of water before the ceiling shows anything, and then release it slowly for days. A tank leak and a pipe dripping in the loft can both look like a one-off stain that keeps coming back. A loft that has been converted adds new pipe routes and boxed sections, covered in water leaks after a loft conversion.
Water near ceiling light fittings and cables is a safety issue. If water is dripping through a light fitting or you can see it near wiring, stay out of the room. Closing the stop tap stops the refill but does not stop a leaking tank, which keeps draining through the ceiling. Switch off the lighting circuit at the consumer unit only if you can reach it dry, and phone a plumber to isolate or drain the tank, and an electrician if fittings are wet.
Which methods are used, and where they fail
Moisture mapping on the ceilings shows where water has gone. Thermal imaging shows cold patches that suggest wet insulation or a cold pipe, but it can be misled by insulation depth and by a cold loft in winter. Both are indicators. They narrow the search and do not name the joint.
A pressure test separates a leak in the pipework from a valve that is passing. Tank-fed pipework runs at low pressure, so a small leak can be quiet, and acoustic detection is less useful there than on a mains pipe. That is a real limit of the method, and the report says so when it applies. Gravity-fed pipework behaves differently from mains-pressure pipework, and the choice of method follows from that.
An endoscope can look behind a tank fitting or into a boxed section through a small opening. It is used when the alternative is lifting boards or cutting plasterboard. After a frost, the thaw-day log shows what to record while the ice melts, which helps the survey that follows.
What it costs and what is not included
A loft survey sits inside the £580 package for locating a leak when the tank, the pipework and the ceilings below are all in one property, with the total known before the visit. Work that runs longer is charged at £180 an hour, which is a fixed hourly rate that cannot rise on the day. No VAT is charged.
No find, no fee applies when a live leak inside your own property cannot be located, and the no find, no fee page sets out the boundary. Hourly rate or package compares the two ways of paying. The survey locates and reports. Preparing for a leak detection visit lists what to clear and find beforehand. A small repair, such as tightening a fitting or replacing a small part on the pipe, can be done on the same visit once the leak is found, agreed first; A larger repair is quoted before any work starts, and the leak is stopped in the meantime. Access openings and making good are separate, and what is included sets out what is and is not covered.
A stained ceiling below the loft can lead to an escape of water claim. Cover depends on the policy and the insurer decides; see insurance-covered leak detection.
Sources
The Water Supply (Water Fittings) Regulations 1999, Schedule 2, paragraph 16 (an effective adjustable valve shutting off the inflow below overflow level, and a servicing valve on the inlet next to a storage cistern), as published on legislation.gov.uk, read October 2026. The legislation is the authority.
Questions customers ask
Can you check a loft tank without going into the loft?
Partly. The hatch gives a view of most tanks, and moisture readings on the ceiling below show where water has gone. Anything beyond the reach of the hatch needs a safe route in, so boards or a clear line of joists matter.
Is a dripping overflow pipe a leak?
It is a sign that water is getting into the tank faster than it leaves, usually a float valve that is not shutting. See loft tank overflow dripping for what the position of the drip tells you.
Will the survey tell me whether it is condensation?
Often yes. Condensation forms on cold surfaces, is worst in cold weather and leaves no single wet joint. A pressure test and readings from a dry comparison area separate it from a leak, and the wet-pipe page shows the same test at home.
Do you replace float valves or repair tanks?
Small parts, yes. Replacing a small part such as a float valve can be done on the same visit once the fault is found, agreed with you first. A larger repair is quoted before any work starts, and the leak is stopped in the meantime, for example a failed tank, and the written report shows where the fault is. See leak repair after detection.
How do you tell a failing float valve from a leaking tank?
The tank level and the overflow are watched with every draw-off point quiet. Water running at the overflow with nothing in use points at the float valve. A normal level with a wet ceiling points at a joint or pipe, which a pressure test then separates from condensation.
What does a loft survey cost?
The £580 package applies when the tank and the leak are in one property, and the total is known before the visit. Work that runs longer is charged at £180 an hour, a fixed hourly rate that cannot rise on the day. No VAT is charged. Larger repairs and access openings are quoted separately.