A stain on the ceiling: finding a slow leak
Updated 1 October 2026 · 2 minute read
The slow leaks are the ones that do the damage. A burst pipe gets noticed straight away. A weeping joint under a bath can drip for months before it shows up as a brown ring on the ceiling downstairs.
First, what is above the stain?
Go upstairs and stand over the stain. Most of the time it is under one of these:
- A bath or shower. Often not the pipework at all, but failed sealant letting water run behind the bath panel or tray.
- A toilet. A worn seal where the pan meets the waste pipe, or a weeping connection on the cistern.
- A basin. The waste trap or a tap connection underneath.
- A radiator. A valve or a joint dripping slowly onto the floorboards.
- Nothing obvious. Then it is likely pipework running under the floor.
Checks you can do
- Use the room above and watch. Run the bath or shower for a few minutes, then check the ceiling. If the stain darkens, you have found the area.
- Dry and feel. Wipe under the basin trap, the toilet connections and the radiator valves with a dry tissue. Any damp shows straight away.
- Check the sealant. Gaps or black, peeling sealant around a bath or tray let water through every time it is used.
- Look at the water meter, if you have one, with every tap off. If it is still moving, water is going somewhere.
When to stop and call us
If the ceiling is sagging, bulging or the stain is spreading quickly, turn the water off at the stop tap and do not wait. Otherwise, take a photo of the stain and of the room above.
How we find and fix it
We start at the most likely source and work outwards, so we lift as little as possible. Weeping joints, worn seals and tired trap connections are everyday jobs for us across Bridgend. Where the leak is somewhere we cannot see without opening up, we tell you why before we lift a board, and you get the price before we start.
Send us a photo of the stain, or read about a toilet that keeps running.
Keep reading
- How a plumber in Bridgend prices your job Why you will not find a plumbing price list here, what we need from you to price a job, and why the price is agreed before we start.
- Dripping tap? Washer, cartridge or a whole new tap How to tell what kind of tap you have, why it drips, and when a repair is worth it versus a new tap. A plain guide from a Bridgend plumber.
- Toilet keeps running? What is going on in the cistern The three usual reasons a toilet keeps filling or trickling into the pan, what you can check safely, and when to call a plumber in Bridgend.