Washer-dryer, or separate washing machine and dryer - which is the best?

Separate appliances are definitely best because the work load is shared between the two machines, and you can be drying one load whilst washing a second.

Washing clothes, and tumble drying clothes, are two totally separate jobs, which need different sized drums. In order to wash clothes effectively, the clothes need to rub against each other. A washing machine's drum size is designed for this to happen. Conversely, to tumble dry clothes effectively the clothes need plenty of space to be able to fall through the hot air. This is why a tumble dryer has a larger drum than a washing machine.

Even though these days it's possible to buy washing machines with really large drums you still need to have less laundry in to tumble dry than the washing machine is capable of washing.

So how do washer dryers work?

Combined washer-dryers have exactly the same sized drum as a normal washing machine, so with a full load inside, in order to get the clothes to fall through the hot air you just have to take some of the washing out first. This is where the inevitable compromise lies (as with most thing's designed to do more than one job) If you are only washing a small load anyway then you can allow the washer dryer to continue onto tumble dry straight after the final spin, but of course you would have to wait until they are finished drying (which takes longer on a washer dryer) until you can start washing a second load. Bearing all this in mind, washing and tumble drying a full load of towels or sheets, where you would need to remove up to half the load after the main wash and then tumble dry in two separate loads, is going to take several hours.

Are washer dryers less reliable than a washing machine?

They should be, they have more parts and do more work, to expect different is unrealistic. But are they less reliable than a separate washer and tumble dryer combined? - That is a much fairer question. According to Which? - Best washing machine brands reports washer dryers do break down more than washing machines, but they don't appear to qualify this by saying whether they break down any more than a washing machine and a tumble dryer.

For all we know, a washer dryer may not on average break down any more than the combined separate machines together. My feeling, to be fair, is that they probably do, but not excessively so. The Which? reliability reports do appear to unfairly compare a single machine doing two jobs with a machine doing only one.

What if the dryer part of a washer-dryer breaks down?

There is a common belief that if you have a washer dryer and it breaks down you lose two machines. This is used as a good reason to avoid them. But logically, if the washing machine part breaks down what use is a tumble dryer anyway? And if the tumble drying section breaks down on a washer dryer you still have the washing machine working. It is very rare for a dryer fault to stop the washing machine working.