Check the warranty before you pick up the phone
This page starts with the boring thing because it is the thing that saves money. A new flat normally has two overlapping protections: a defects or snagging period with the developer, typically covering the first stretch after completion, and a longer structural warranty from a warranty provider. What each covers and for how long is set out in your own warranty documents and your purchase paperwork, and there is no universal answer.
If a heating loop embedded in screed has failed, that is exactly the kind of thing those arrangements exist for. Instructing your own contractor to cut the floor before notifying the developer or the warranty provider can prejudice the claim. So: read the documents, notify in writing, and keep the notification. Then, if they will not act or the cover has expired, the job becomes an ordinary one and we are happy to do it.
We would rather tell you this and not get the work than take the job and cost you a warranty claim.
What the symptom looks like, and why it is so quiet
Underfloor heating in a modern Nine Elms flat is usually plastic pipe, clipped to insulation over the structural slab and buried in a liquid anhydrite screed, typically fifty millimetres or so of it, with a tiled or engineered timber finish on top. It is a good system. Its one bad habit is concealment.
A pinhole in a UFH loop does not appear as a puddle. Screed is absorbent and the floor it sits in is warm, so for weeks or months the water goes in and evaporates out and nothing shows. The symptoms you get instead are indirect:
- System pressure dropping and needing topping up, weekly rather than annually.
- One room or one zone noticeably cooler than the rest, or slower to come up.
- A patch of floor that is warmer than its surroundings when the heating has been off for hours.
- Tiles lifting, grout darkening, or an engineered board cupping at the edges in one area.
- In a flat above someone else, a complaint from downstairs long before you see anything yourself.
The warm patch on the floor is the useful one, because it is the only symptom that is spatially specific.
Narrowing it to one loop, before touching the floor
This is the step that makes the difference between cutting one small hole and cutting several.
A UFH system is a set of loops radiating from a manifold, usually in a cupboard or a utility space. Each loop has its own flow and return with isolating valves. That means the system can be divided against itself: isolate every loop, pressurise the manifold, and see whether it holds. If it holds, the loss is not in the buried pipework and attention moves to the boiler, the heat interface unit, the valves or the visible pipework in the cupboard. If it does not hold, loops are opened one at a time until the pressure starts falling again.
That narrows a whole apartment to one circuit before anyone has been near the tiles, and it is the reason a competent UFH detection visit spends its first hour at the manifold and not on hands and knees with a camera.
Finding the point of loss within the loop
Once it is one loop, three techniques do the work, in this order.
Thermal imaging with the loop driven
Run warm water through the suspect loop only and the pipe route images clearly through tile and screed. A leak shows as a diffuse bloom that does not follow the pipe geometry, usually slightly offset from the run because water tracks along the underside of the screed before it does anything visible.
Moisture mapping
Non-destructive meters across the floor build a contour of where the screed is wet. On its own it is misleading, because screed wicks and the wettest reading is often at a threshold or a wall junction where the water has collected rather than where it entered. Combined with the thermal image it is very good.
Tracer gas
Where the first two disagree, or where the floor covering defeats thermal imaging, the loop is drained and a hydrogen and nitrogen tracer mixture is pushed through it. It escapes at the fault, works up through the screed and is picked up at the surface. It is the most precise method available on a buried loop and it touches nothing.
Cutting the floor, which is the part people dread
Done properly this is a neat operation. The tile or board over the located point is lifted, the screed is cut back in a small square, the damaged section of pipe is exposed, cut out and replaced with a proper buried-grade coupling rated for the job, the repair is pressure-tested before anything goes back, and the screed is made good with a compatible repair compound and the finish relaid.
Two honest caveats. Matching a tile or an engineered board in a development where the original was specified five years ago is sometimes impossible, so it is worth asking the building manager whether the developer left attic stock; many did. And anhydrite screed needs the right repair material, not a generic sand and cement patch, because the two do not get on chemically.
We carry out the repair and the reinstatement as one job rather than leaving you to find a tiler afterwards.
Things that look like a UFH leak and are not
- A failed expansion vessel. Pressure that climbs high when the system runs and falls below normal when it cools is usually a vessel that has lost its charge, not a leak. Rule it out before anyone talks about cutting a floor.
- A heat interface unit. Many of these buildings are on communal heat networks, and the HIU in the cupboard has its own plate heat exchanger, valves and strainer. A weep there presents as system pressure loss with no floor symptoms at all.
- Condensation under a cold zone. An unheated area next to a heated one can collect condensation at the slab interface and darken a floor finish without any water escaping from anywhere.
- Water from the flat above. A wet floor is not necessarily a wet floor from below. If the pressure is holding steady, the water is coming from somewhere else.
If the gauge is the main symptom, start with pressure dropping with no visible leak.
