Replacing a mixer tap is one of those jobs that's well within reach for a competent DIYer — but the water isolation step is where people come unstuck. Get that right and the rest is straightforward. This guide covers both the isolation and the installation in full.
Step 1 — Isolate the water supply
How you isolate the water depends on your heating setup. The quickest way is to find the two chrome isolation valves under the basin or sink — they have a slot for a flat-headed screwdriver. Put the screwdriver in the slot and turn a quarter turn to the right so the slot sits horizontally. Open both taps to drain any remaining water from the pipes, then close the taps again. You're ready to disconnect.
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Step 2 — Disconnect and remove the old tap
Locate the connections under the sink
Look under the basin or sink. You'll see the flexible tap connectors running from the base of the tap down to the isolation valves or compression straights. Find the nuts connecting these and with an adjustable spanner (and a small rag to catch any residual water), turn them to the left until fully disconnected.
Undo the back-nut
Take your basin box spanner (or tap back-nut spanner) and slide it up over the hexagonal nut securing the tap to the basin. Turn to the left until it's free — the metal and rubber washers will fall away. If the nut is corroded or seized, soak with penetrating oil and leave for a few minutes before trying again.
Lift the old tap out
The tap can now be lifted up and out. Note: the nuts on both flexible pipes together are often too wide to come up through the hole. Either pull one pipe up and through before the other, or unscrew the flexible hoses from the base of the tap before lifting it clear.
Step 3 — Install the new tap
Your new mixer tap should have come with two flexible mono tap connectors that screw into the holes in the base. There'll also be a threaded metal piece that screws into the remaining hole, and a thin rubber or chrome washer that sits between the base of the tap and the surface of the sink.
Position the new tap
Place the tap body on top of the sink hole with the flexible hoses and the threaded metal piece hanging down through it. Fit the rubber or chrome washer between the base of the tap and the sink — this is what creates the seal.
Secure the tap from underneath
Go back under the sink with the C-shaped metal washer, rubber washer and the brass or copper hexagonal locking nut. Push the rubber washer up over the threaded metal section hanging down, followed by the metal washer. Holding them in place with one hand, start screwing on the locking nut by hand until it won't go any further. Then use the box spanner to tighten fully — keep an eye on the tap body alignment above as you go to make sure it doesn't rotate out of position.
Connect the supply pipes
Locate the two isolation valves or compression straights and screw the nuts on the end of the flexible hoses onto them. Make sure hot is on the left and cold on the right — the standard convention. Hand-tight first, then a further half-turn with the adjustable spanner. Don't overtighten.
Turn the water back on and check
Put the screwdriver back into the isolation valve slots and turn a quarter turn back to the left so the slot sits vertically again. Slowly open the taps and run water briefly. Then check every connection carefully — underneath the sink, around the base of the tap, along the flexible hoses. A small leak left overnight can cause serious damage. If anything is dripping, tighten slightly or turn off and call a plumber.
Not confident with the isolation valves, or working with older pipework? Give John a call on 07877 486 939 — tap replacements are one of his most common jobs across Stirling and Dunblane. See the tap fitting service →
JHDS Plumbing & Tiling accepts no responsibility for damage caused following our guides. If in doubt, contact a professional before starting.
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