Why does my tumble dryer take so long to dry a load?

A tumble dryer removes water by pushing warm air through fabric and taking the moisture away. Everything that makes it slow is a restriction on one of those two things: either the air is not moving, or the load arrived with far more water in it than it should have. That is why the diagnostic runs outward from the washing machine rather than starting at the dryer.

Safety

What you'll need

• Vacuum with a crevice tool
• A soft brush
• Warm soapy water, for the filter
• A bowl, for rinsing the condenser unit (optional)
• A torch (optional)

Step by step

1. Start at the washing machine spin speed.A load spun at 800 arrives with roughly half as much water again as one spun at 1400. That difference alone can add a third to the drying time and is entirely free to fix.
2. Check how full the drum is.A dryer needs air to move through a tumbling load, so no more than about two thirds full. A packed drum does not tumble, so the outside dries and the middle stays wet, and the machine keeps running.
3. Clean the lint filter and look at it against the light.Peel the lint off, then hold it up. If the mesh looks hazy rather than clear, wash it in warm soapy water and dry it fully. Fabric conditioner leaves an invisible film that restricts airflow badly while the filter appears clean.
4. Vacuum the filter housing underneath.Unplug the machine first. There is a recess below and behind the filter that collects a felted mat of fine lint which cannot be pulled out by hand. A crevice tool reaches it. Almost nobody cleans this and it is a leading cause of gradually lengthening cycles.
5. On a condenser dryer, remove and rinse the condenser unit.Usually behind a flap at the bottom front. Rinse it under a tap from both sides until the water runs clear, shake it out and let it dry fully before refitting. Monthly is the right interval.
6. On a heat pump dryer, clean the secondary filter and the evaporator.Behind the plinth panel at the bottom front. There is a second filter most owners do not know exists, and a set of fine metal fins behind it. A grey mat across those fins is the classic reason a heat pump cycle stretches from two hours to five. Follow the manual — the fins are delicate and must not be bent.
7. Empty the water container every load.A full container stops the cycle, often part way through, so the load is found damp and the machine appears to have failed. Many machines can be plumbed to the waste instead.
8. On a vented dryer, check the hose and the outside grille.Disconnect the hose and look through it. Kinks, crushing behind the machine, excessive length and accumulated lint all choke it. Outside, check the grille flap opens and is not blocked by debris, cobwebs or a nest.
9. Check the room the machine is in.Condenser and heat pump dryers need a supply of cool room air to condense against. In a small unventilated cupboard or a hot utility room they dry much more slowly. Open the door or fit ventilation.
10. Wipe the moisture sensor bars if the machine has them.Two metal strips, usually in the drum or on the filter housing, that measure how wet the load is by conductivity. Fabric conditioner and limescale coat them so the machine reads the load as wetter than it is and runs on. Wipe them with a cloth and a little white vinegar.
11. Separate a gradual decline from a sudden one.Gradual is airflow, and the checks above will find it. Sudden — the machine tumbles but the air is barely warm, and the load is no drier after two hours — points at the heating element or a thermostat, which are behind the casing.
12. Stop at the casing.Elements, thermostats, thermal cut-outs and the heat pump's sealed refrigerant circuit are engineer work. Note any error code and the model number from the rating plate and hand it over.

Tips

• Dryer balls genuinely shorten cycles by keeping the load open so air can move through it, and they replace dryer sheets, which add to the film on the filter.
• Drying similar items together matters more than people expect. A load of towels mixed with T-shirts will either leave the towels damp or bake the T-shirts, and sensor programmes handle mixed loads badly.
• If cycles have been getting longer over a year, do all the airflow checks in one session rather than one at a time. There is usually more than one restriction.
• Cutting back on fabric conditioner reduces both the filter film and the coating on the sensor bars, which are two of the commonest causes on this list.

Common mistakes

• Cleaning the visible filter and stopping there — The housing beneath it, the condenser unit and the heat pump's secondary filter all restrict airflow just as effectively, and none of them is visible when the filter is out.
• Loading the dryer like the washing machine — A dryer needs tumbling space and airflow through the load. Two thirds full is the working limit, and a full drum can double the cycle time while drying unevenly.
• Treating a long cycle on a heat pump machine as a fault — Heat pump dryers run cooler and are meant to take longer than a vented machine. The fault is when the time keeps growing, not that it is longer than a hot dryer's.

If it doesn't work

Questions people ask