Do this first
- Press it, gently, with the back of a finger. Soft, cool and slightly giving means water is still there. Dry, hard and cool-neutral means it has stopped, at least for now. Do not press hard on a stain that has any sag in it.
- Check the electrics before you touch anything else if the stain is near a light fitting or a downlight. Switch that circuit off at the consumer unit rather than testing the switch.
- Draw round the edge in pencil and write the date on the ceiling. It will be painted over later. This one habit turns a vague worry into a measurable fact, and it is the first thing a good engineer will ask for.
- Photograph it with the date visible and take another photograph a week later from the same spot.
- Read the water meter with everything off for thirty minutes, and read the boiler pressure gauge cold on two consecutive mornings.
- Check the weather correlation. Note whether it grew during rain or during a dry week.
- Do not paint it, seal it or stain-block it yet. Over an active leak it bleeds back through within weeks and you have lost the only record of how it was spreading.
Live, historic, or not plumbing at all
A stain is evidence of a past event, not proof of a present one, and the three cases need completely different responses.
| Finding | What it means | Next step |
|---|---|---|
| Soft, cool, edge beyond your pencil line a week later | Live leak, still running | Find the source before anything is decorated |
| Hard, dry, sharply ringed, unchanged after a fortnight | Historic. Something leaked and was fixed, or stopped | Stain-block and redecorate |
| Grows after rain, fades in dry weather, top floor or near an external wall | Roof, flashing, parapet or gutter | Roofer or the freeholder, not a plumber |
| Meter moving with everything off, or boiler gauge falling | Plumbing, whatever the stain looks like | Detection |
| Grey or black mould rather than a brown ring, in a cold corner | Condensation | Ventilation and heating pattern |
The ring is worth reading properly. A sharp brown tide line with a defined edge is a stain that dried at that boundary, which is the signature of an event that ended. A soft, diffuse edge that you cannot quite find is water still moving through the plaster. Multiple concentric rings mean it has wetted and dried repeatedly, which points at something intermittent, typically a shower, a bath or an appliance above rather than a pressurised pipe.
Position lies. Water runs along the top of a joist until it meets a board joint or a screw, so the stain can be a couple of metres from the leak and on the wrong side of the room. That is why a meter test is better evidence than a pencil line pointing at the bathroom. If the stain is under a bathroom, a shower leaking through the ceiling gives you a timing test to run, and if water is actually arriving rather than just staining, start at water coming through a ceiling.
What the repair involves
Detection begins with moisture mapping across the whole ceiling rather than at the stain, because the wettest point and the stained point are rarely the same. Thermal imaging picks up hot pipe runs in the void and the evaporative cooling around a wet area. Where the loss is pressurised, the circuits are isolated and pressure tested to attribute it, and tracer gas goes in last where nothing else can see the pipe.
Once the source is repaired, the ceiling gets treated as a ceiling rather than a stain. Anything blown or soft is cut back to sound board, the void is dried, new board is fixed, taped and skimmed, and the whole ceiling is stain-blocked and painted corner to corner, because a patch in the middle of an old ceiling shows under every light in the room. That is ceiling leak repair, and if you are claiming, the insurance claims hub covers what the report needs to say.
When it is not us
- Hard, dry, unchanged for a fortnight, meter static, gauge steady. Stain-block it and paint. There is nothing to find.
- It tracks the weather. Roof, gutters, pointing or flashing. That is a roofer, and in a block it is the freeholder's structure.
- Black spotted mould in a cold corner with no water history. Condensation. Ventilation, extraction and background heat.
- A single small ring under a bathroom that has since been resealed. Likely historic. Watch it for a fortnight before spending anything.
- The source is upstairs in someone else's flat. Start with access and liability: a leak from the flat above.
- You rent. Report it in writing with your photographs and the dated pencil line. It is the landlord's to investigate.