Why does my washer dryer need the cold tap on to dry?

It surprises people that a drying cycle consumes water, and it prompts a lot of unnecessary fault reports when someone has sensibly turned the tap off between washes. Understanding the mechanism explains not just why the tap matters but also why washer dryers cost more to run than the electricity figure suggests, and why a heat pump model is worth the premium.

What you'll need

• The manual, to confirm which condensing method your model uses

Step by step

1. Work out which type your machine is.The manual will say, and the specification usually quotes a water consumption figure for the drying programme. If the drying cycle has a water figure at all, it condenses with water.
2. Understand what the water is doing.It runs as a cold film down the outer drum wall. Steam from the load hits that cold surface, condenses, and the resulting water drains away with the cooling water. No mechanical condenser unit is involved, which is how it fits in the space.
3. Leave the cold tap fully open during drying.This is the practical point. With the tap closed the machine cannot condense, so it recirculates increasingly humid air, dries very little, and often puts steam into the room instead.
4. Expect the water consumption to be real.The drying phase can use a substantial quantity over its full length. On a metered supply this is a genuine cost that no electricity figure captures.
5. Recognise the alternative types.Air-condensing washer dryers condense against room air and use no extra water; heat pump washer dryers recover the heat as well and use far less electricity. Both are more expensive to buy and better to own.
6. Do not restrict the tap to save water.A partly open tap gives poor condensing and a much longer cycle, which usually costs more in electricity than it saves in water. Either use the machine as designed or change the machine.
7. Check the waste arrangement if drying is poor with the tap on.The cooling water has to leave freely. A waste hose that is too high, kinked or partly blocked interferes with condensing as well as with draining.

Tips

• Turning the taps off when you go away is good practice for flood risk. Just remember to open the cold one again before running a drying cycle.
• If you are on a water meter and use the drying function often, the drying water figure in the manual is worth putting through the same arithmetic as the electricity. It sometimes changes the case for a heat pump model.
• A washer dryer that steams up the kitchen during drying is telling you it is not condensing. The tap is the first thing to check, the waste hose height the second.

Common mistakes

• Closing the cold tap and then reporting a drying fault — It is the commonest false fault on this type of machine. Nothing is broken; the condensing mechanism has simply been switched off at the wall.
• Assuming the drying phase is electricity only — On a water-condensing model the drying phase has its own water consumption, which does not appear anywhere in the energy label figure.

Questions people ask