Dehumidifier not collecting water? Causes and fixes

Check the room humidity and the setpoint first

Every dehumidifier with a humidistat switches its compressor or heater off once the room reaches the target you set. If the target is 60 % and the room is already at 55 %, the fan may keep running while nothing is extracted. Look at the displayed humidity, then set the target 10 points below it, or select continuous mode, and leave it for an hour.

Remember that the built-in sensor reads the air around the machine, not the far corner of the room. In a warm, recently heated room in winter, humidity can sit at 45 to 55 % and a dehumidifier will collect very little. That is a good result, not a fault. Our guide to dehumidifier humidity settings has a table of sensible targets by room and season.

1. 1

   Read the humidity shown on the display.

2. 2

   Set the target well below it, or choose continuous mode.

3. 3

   Close doors and windows in the room.

4. 4

   Run for at least an hour, then check the tank.

Is the room too cold for a compressor model?

Compressor dehumidifiers work by cooling air over a cold coil until the water vapour condenses. As the room gets colder, the gap between the air temperature and the coil temperature shrinks and extraction falls sharply. Below about 15 °C most compressor machines collect noticeably less, and below about 10 °C many spend much of their time defrosting instead of collecting water.

If the machine is in a garage, conservatory, unheated spare room or cellar, the cold is the most likely reason for an empty tank. A desiccant dehumidifier uses a zeolite wheel and a heater instead of a cold coil, so its output stays far steadier in the cold. See the best dehumidifiers for garages and cellars if this matches your room.

Filter, airflow and placement

A clogged filter starves the coil of air, so less moisture reaches it. Most dehumidifiers have a washable mesh filter behind a grille that should be cleaned every few weeks in heavy use. Vacuum it or rinse it as the manual says, and let it dry fully before refitting.

Placement matters too. A machine pushed against a wall, behind a sofa or under a curtain recirculates its own dry air. Give it clear space on the intake and outlet sides, usually around 20 to 30 cm, and keep it away from a radiator that will warm the air sensor and confuse its reading. Our guide on where to put a dehumidifier covers this in more detail.

Tank, float and drain hose checks

If the display shows a full tank warning while the tank is empty, or the machine stops after a few minutes, the tank may not be seated properly or the float inside it may be stuck. The float is a small plastic part that rises with the water and trips a switch. Remove the tank, check the float moves freely, wipe away any slime and push the tank back until it clicks.

With continuous drainage, water goes down the hose rather than into the tank, so an empty tank is normal. Check that the hose runs downhill all the way, has no kinks and is not sitting in water at the far end. A hose that rises at any point can back up and stop the flow.

• Tank pushed fully home
• Float moves freely and is clean
• Drain hose falls continuously with no kinks
• Hose outlet not submerged

Signs of a real fault

If the room is warm (above about 18 °C), the humidity reads above 65 % and the machine is set to continuous, a compressor dehumidifier should collect a visible amount of water within an hour or two. Carefully feel the air from the outlet after 20 minutes. On a working compressor model it should feel slightly warmer than the room. If the outlet air is the same temperature as the room and the compressor never seems to start, the compressor, its relay or the refrigerant charge may have failed.

Those parts are sealed and not user serviceable. Contact the maker or the retailer, especially if the unit is under warranty. Before you do, note the model, the room temperature and humidity, and any error code or warning light, because support teams will ask for them.

Note:Unplug the dehumidifier before removing panels, filters or the tank, and never try to open the sealed refrigerant circuit yourself.

When a different machine makes more sense

Sometimes the machine is fine but it is the wrong type for the space. A small compressor unit in a cold, single glazed bedroom will struggle all winter. A desiccant model in a warm living room will use more electricity than it needs to. Match the type to the room temperature first, then the size to the damp. Our desiccant vs compressor comparison explains the trade-off, and the best dehumidifiers for UK homes covers both types.

See the best dehumidifiers for UK homes →

Frequently asked questions

Why is my dehumidifier running but not collecting water? Usually because the room is already below the target humidity or too cold for a compressor coil. Lower the setpoint or use continuous mode, and check the room is above about 15 °C.

How much water should a dehumidifier collect in a day? It depends on how damp and warm the room is. In a heated home in winter, a few hundred millilitres to a couple of litres a day is common. The litres a day on the box is measured at warm, humid test conditions, so real figures are lower.

Can a dirty filter stop a dehumidifier collecting water? Yes. A blocked filter cuts the airflow over the coil, which reduces extraction and can also lead to frost forming on the coil. Clean it as the manual describes.

Is it broken if the tank is empty in the morning? Not necessarily. Check the humidity reading first. If it is below your target, the machine has done its job and simply switched the compressor off.