You probably use your kitchen faucet on a daily basis, and when it starts leaking, rather than fitting new cartridges, you can replace a two-handled unit with a functional single handle mixer tap that blends hot and cold water through a central spout. Although installing a mixer tap still requires two connections, check underneath to see whether your sink has one, three or four holes to ensure that you buy a replacement that fits; and if you have spare holes, you can install a soap dispenser, sprayer or hot water dispenser while you have the opportunity.
Position a fluorescent lead-lamp on the floor of the cabinet to provide you with enough light to work. Turn off the faucet water supply at the shut-off valves and release any remaining pressure in the lines by opening the faucet.
Place a bucket under the shut-off valves and undo the faucet supply hose compression fittings with two opposing adjustable wrenches.
Push a pair of channel pliers up behind the sink, position the jaws over the wide plastic nuts holding the faucet in place. Twist the pliers counterclockwise to loosen the nuts. Reach up and spin the nuts off the faucet by hand.
Pull the old faucet and supply hoses out of the sink. In some cases, an existing mixer faucet with a single pull-down handle is fitted with separate attaching bolts. If this is the case, you need to first remove the faucet handle by undoing the attaching screw and lifting off the faucet body tube, and then prying off the decorative base plate to access the bolts. In addition, you need a helper to hold the nuts from underneath with a wrench while you remove the bolts from the top.
Pry the separate decorative base plate off with a putty knife if applicable. Scrape off any remaining caulking compound from the surface with the putty knife, and wipe the area clean with a rag.
Place the rubber gasket supplied with the new faucet over the underside of the decorative faucet base plate. Roll out a length of plumber's putty and press it into the groove around the rim of the rubber gasket. Position the base plate and gasket over the three holes in the sink and press the plate firmly down.
Attach two new flexible water supply hoses onto the inlets on the base of the new faucet. Tighten both compression fittings securely with the adjustable wrench, but don't damage the rubber washers by over-tightening.
Guide the faucet base and hoses through the hole in the base plate and into in the sink. Screw the wide plastic nuts supplied onto the two outer faceplate retaining bolts protruding through the bottom of the sink. Thread the large faucet securing nut and washer over the supply hoses and onto the faucet base, and tighten all three nuts securely with the channel pliers.
Connect the water supply hose compression fittings onto their respective shut-off valves. Tighten both compression fittings firmly with two opposing adjustable wrenches, but do not over-tighten.
Scrape off the excess putty squeezed out from under the decorative base plate with the putty knife, and wipe the surface clean with a rag. Turn on both water supply shut-off valves. Open the faucet mixer tap halfway and allow both hot and cold water to run into the sink.
Check underneath the sink to ensure that there are no leaky compression fittings. If you detect any leaks, tighten the compression fittings another quarter turn to stop the leaks and to complete the installation.
Although the above description applies to a typical, single-handled mixer tap installation, your particular faucet assembly details may differ slightly from the above steps. Please read the installation instructions carefully before starting the project.