How do I fit a new basin tap?

Changing a tap is straightforward everywhere except behind the basin, where there is no room for a hand and no line of sight. Everything that makes this job manageable is about preparation before the awkward part begins.

What you'll need

• The new tap and its fixings
• Flexible tap connectors of the right length and thread
• A basin wrench or box spanner
• Isolating valves if not already fitted
• Penetrating spray, cloths and a bowl

Step by step

1. Check what connections the new tap uses.Most modern basin mixers have flexible tails already attached, usually 10mm or with a half-inch female thread. Older taps have a half-inch male thread and need separate connectors.
2. Fit isolating valves if there are none.Without them you have to drain the whole house every time. Fitting them is a job in itself but it transforms this and every future repair.
3. Turn the water off and drain the tap.Close both isolating valves, open the tap fully to drain it, and leave it open. Put a bowl and cloths underneath.
4. Disconnect the supplies.Undo the tap connectors at the tap end. Expect a cupful of water even after draining.
5. Free the backnut.This is where the job is won or lost. Penetrating spray, time, and a basin wrench that reaches up behind the basin. On a badly seized nut, cutting the old tap tail with a mini hacksaw is a legitimate last resort.
6. Clean the basin surface completely.Scrape off old sealant and limescale so the new tap's washer or gasket sits flat. A dirty seat is why new taps rock.
7. Fit the new tap loosely first.Drop it in with its rubber gasket, thread the fixing on by hand, and check the tap is square to the basin before tightening.
8. Tighten the fixing evenly.Modern taps often use a threaded rod and a plate rather than a big backnut. Tighten evenly and firmly — but ceramic basins crack, so firm rather than hard.
9. Connect with flexible tails.Buy them slightly longer than you need so they curve rather than kink. Hand-tighten onto the tap's fibre washers, then a quarter turn with a spanner.
10. Turn on slowly and check everything.Open the isolating valves gradually. Run both hot and cold, check every joint with a dry finger, and check again an hour later.
11. Seal the base if the tap is not gasketed.A thin ring of silicone under the tap base stops water sitting under it and getting into the fixing.

Tips

• Buy a basin wrench before starting, not halfway through. It is inexpensive and the job is genuinely difficult without one.
• Take a photo of the existing connections before dismantling. Thread sizes are hard to recall in a cupboard.
• Empty the cupboard completely and put a towel down. You will be lying in it.

Common mistakes

• Overtightening the flexible connectors — The fibre washer does the sealing. Overtightening crushes it and distorts the thin tail, so the joint weeps and the tail can eventually split under pressure.
• Reusing the old flexible tap connectors — The rubber inside perishes and the braid corrodes where it has been bent. They are cheap, they fail suddenly, and a burst tail floods a house.

If it doesn't work

Questions people ask