Leak Sensors and Where a Flat Floods Quietly

The expensive leaks are the slow ones, because nobody sees them.

A burst pipe is loud, obvious and dealt with in minutes. A weep from a washing machine hose runs behind the appliance into the floor for weeks, and by the time it announces itself the damage is to the floor, the cupboard, the ceiling below and somebody else's flat.

Cost tracks time undetected, not flow rate. Which is why a device that tells you early is worth more than one that limits how fast it arrives.

A note on this guide: this rests on where plumbing leaks typically originate and on how these sensors work, not on products tested here. Anything involving your incoming supply or a boiler is a plumber's job. See how we test.

The five places, in rough order

1. Behind the washing machine or dishwasher. Hoses, their connections, and the door seal. The appliance hides the leak and stands on the evidence.

2. Under the sink. Trap connections, isolating valves, and the waste. It is also the cupboard holding everything you own in plastic bottles, which absorbs the first few weeks of it.

3. At the boiler or hot water cylinder. Often a slow weep from a valve or fitting.

4. Radiator valves. Particularly after being turned for the first time in a year at the start of the heating season.

5. Behind the toilet, at the pan connector or the cistern feed.

Every one of them is hidden. That is not coincidence — the visible ones get fixed the same day.

This page contains affiliate links. If you buy through them, Ugly Fixes may earn a commission at no extra cost to you. Products are selected independently.

What actually matters

1. Putting the sensor where the water goes

On the floor, at the lowest point water would reach. Not on the appliance, not behind it at height, not on a shelf above the risk.

Water runs downhill and pools. If the sensor is not sitting where the puddle forms, it is decoration.

2. Connected versus local, which depends on your day

A local alarm works if someone is home. If the flat is empty from eight until six, a sounder in an empty kitchen achieves nothing and a notification achieves everything.

That is the whole decision between the two types.

3. A tray to contain what the sensor detects

A tray and a sensor solve different halves of the problem: the tray limits and directs the water, the sensor tells you it is there. A sensor sitting in a tray is the arrangement that does both.

4. Knowing which problem you have

Water on a floor is not always a leak. Condensation, a blocked drain and rising damp all present as damp and have completely different fixes.

The full argument for telling those apart before spending anything is in is the wall damp, or just cold?

What is free and matters as much

Find your stopcock and turn it. A great many are seized, and people discover this while standing in water. One minute, no cost, and it is the single highest-value action on this page.

Look behind the washing machine twice a year. Pull it out, look at the hoses, look at the floor.

Replace flexible hoses on schedule. They have a service life, they are cheap, and they are the most common failure point on this list.

Know your building's arrangement if you are in a flat — where the isolation is, and who to call out of hours.

The mistake to avoid

Fitting the sensor at a convenient height rather than at floor level. It is the most common installation error and it produces a device that will never fire, because water does not climb.

The second mistake is assuming detection is prevention. A sensor shortens the time a leak runs, which is where most of the cost is — but the hose still needs replacing, and if the flat is empty for weeks at a time an alert nobody reads is not much better than no alert at all.