Using professional cleaners

Particles of dirt walked into the carpet over time can leave it looking grubby and the pile tired and flattened. To remove dirt and refresh the pile, the Australian/New Zealand carpet cleaning standard AS/NZS 3733:1995 recommends a "restorative" clean at least every two years.

Carpet cleaners offer a choice of hot-water extraction (sometimes called "steam cleaning") or dry cleaning.

Hot-water extraction

Hot water is sprayed on to the carpet through a wand that then extracts the water and dirt using a powerful vacuum. Detergent is usually added to the water, to help lift the dirt.

Hot-water extraction can be done with a portable machine or from a truck-mounted system. Portable machines may use your hot-water supply - if they do, they'll take lots of it.

After the treatment's completed, make sure your furniture doesn't come into contact with the damp carpet or you'll get stains. So furniture legs should be placed on plastic squares, and furniture without legs should be lifted on to polystyrene or plastic blocks.

What's good about it

Hot-water extraction is the method recommended by most manufacturers, and it's the standard for restorative cleaning. It removes more dirt, and can be used on stairs and upholstery.

Downside

It takes longer to dry. If an inexperienced operator allows your carpet to get too wet it may shrink, will certainly take longer to dry, and - if the drying process takes too long - may also develop mould.

Dry cleaning

The most common dry-cleaning method is "bonnet buffing" (pictured). This is where a rotary machine with a round shag pad or "bonnet" attached to its base runs over the carpet, which has been lightly wetted with cleaning agent.

Another method is "dry foam", where foam is worked into the carpet by a revolving brush and allowed to dry to a powder that traps dirt particles. The carpet is vacuumed afterwards to remove the residue.

What's good about it

Dry cleaning means your carpet dries quickly - you can use the room almost immediately.

Downside

It's really only "surface cleaning", and isn't as good as hot-water extraction at removing ingrained dirt. Dry-cleaning methods are usually not suitable for stairs, unless the machine is small enough.

DIY hot-water extraction?

You can hire hot-water extraction machines from supermarkets and hire centres. They're usually easy to use, and they're cheaper than calling in a commercial cleaner. But you're unlikely to get the carpet as dry as a professional operator would - and if anything goes wrong you have no comeback.