How to find a water leak in your home
The leak is almost never where the wet patch is. Here is how to narrow it down before anyone starts taking up floorboards.
By Dan, Gas Safe registered engineer6 min read
The first thing worth knowing about a hidden leak is that water travels. It runs along joists, follows the outside of a pipe, and comes out through the first gap it finds. So the damp patch on your ceiling is often nowhere near the thing that is actually leaking. Working back from the evidence properly is the difference between one small repair and a floor taken up in the wrong room.
If water is pouring in right now
Turn the water off at the stopcock, usually under the kitchen sink or near the front door, put something under the drip, and ring me on 07949 353536. Getting the water off is the single thing that limits the damage. Everything else can wait ten minutes.
Step one: is it actually a leak?
Not every damp patch is plumbing. Condensation, a slipped roof tile, blown pointing or a blocked gutter all produce damp that looks convincingly like a leak. A useful clue is timing. Damp that appears or worsens after heavy rain is usually coming from outside. Damp that is the same in dry weather, or that gets worse when the heating runs, is more likely to be plumbing.
Step two: the stopcock test
This narrows it down quickly. Turn off every tap in the house, then find your water meter if you have one and note the reading. Leave everything off for an hour without using any water at all, then read it again. If it has moved, water is escaping somewhere on the incoming supply.
If you have no meter, you can do a rough version by turning the stopcock off entirely for an hour and seeing whether the damp patch stops growing. It is cruder, but it tells you whether you are chasing the mains or the heating.
Step three: mains or heating?
These are two separate systems and it matters which one you are dealing with. If your boiler pressure keeps dropping, the leak is on the heating side: radiators, valves and the pipework that feeds them. If the pressure is rock steady but you have damp, you are more likely looking at the mains, a waste pipe or something around a bathroom.
- Boiler pressure falling: heating system. Check radiator valves for staining and look at the relief pipe outside.
- Pressure steady, damp near a bathroom: often a shower tray, a seal or a waste pipe rather than a pressurised pipe at all.
- Damp low down on a ground floor wall: could be the incoming main, could be rising damp. Worth being sure before digging.
Step four: the places it usually is
After enough of these you get a shortlist. Radiator valve unions are top of it, because they weep slowly for months. Then joints under floors, particularly where pipework was disturbed by a previous job. Then shower trays and bath seals, which fail quietly and soak the floor rather than the ceiling. Then the connections under a sink, which people rarely look at because there is a cupboard in the way.
What is rarely the problem is a copper pipe failing in the middle of a run for no reason. If somebody tells you that on the first visit, ask what led them there.
When to stop and get someone out
If you have narrowed it to a system but not a spot, or the leak is under a floor or behind a wall, that is the point to stop. The cost of a leak is almost never the repair, it is the damage while it goes unfound and the damage caused by looking in the wrong places. I would rather spend the time tracing it than take up your floor on a guess and be wrong.
I trace leaks across Preston, Penwortham, Chorley, Euxton, Clayton-le-Woods, Bamber Bridge, Leyland and Kirkham. If you are not sure whether you are in the patch, ring and ask.
Need this doing?
I am Dan, and I cover Preston and the towns around it.