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Fit a new kitchen tap

  • Writer: Robert Costart
    Robert Costart
  • May 29
  • 3 min read

Updated: Jun 4



 📝 Overview


• Installing a brand-new monobloc kitchen mixer on a stainless-steel or composite sink, including mounting, connecting flexi-tails and commissioning the supply.

• Skill level: 3 / 5 (confident DIYer, cramped plumbing).

• Typical duration: 1½–2 h hands-on.




⚠️ Safety First


  1. Isolate hot and cold feeds with service valves or the main stopcock to prevent flooding.

  2. Open existing tap to depressurise lines and avoid spray-back when fittings loosen.

  3. Wear cut-resistant gloves—sink edges, braided hoses and stud rods are sharp.

  4. Use eye protection while flushing pipework; grit or scale ejects at speed.

  5. Keep electrical leads and appliances clear of the wet area to eliminate shock risk.




🧰 Tools & Materials

Item

Purpose

Adjustable spanner & basin wrench

Undo hose nuts in the cramped void behind the sink

Monobloc box spanner (11 mm or 12 mm)

Reach and tighten the long retaining nut on the tap stud

Flat/Phillips screwdrivers & 2 – 5 mm Allen keys

Remove handle trims or grub screws

Pipe cutter & deburr tool

Trim/clean 15 mm copper tails if repositioning valves

Full-bore 15 mm lever isolation valves

Comply with Water Regs and future maintenance 

Flexible tap tails ½” BSP × 15 mm

Connect tap body to pipework 

PTFE tape & compression olives

Seal threaded or compression joints

Non-setting sanitary silicone & rubber gasket

Waterproof seal between tap base and sink

Plumber’s silicone grease

Lubricate O-rings for smooth swivel and longevity

Bucket, towels, torch & kneeling pad

Contain drips and improve comfort/visibility



📋 Step-by-Step



1. Plan the layout


  1. Measure the sink-deck hole (⌀ 35 mm is standard) and the clearance for lever travel.

    • Why: Ensures the new tap fits without fouling upstands or window cills.

    • Pro-tip: If the worktop has no hole, mark the centre and drill with a sharp 35 mm hole-saw at slow speed; clamp timber beneath to stop breakout.



2. Isolate and drain


  1. Shut both isolation valves or the stopcock, then open the old tap to drain down.

    • Why: Removes pressure so hoses can be safely detached.

    • Pro-tip: If isolation valves are missing, cut the copper and add them now—mandatory under Water Supply (Water Fittings) Regulations 1999. 



3. Remove the old tap (if present)


  1. Undo flexi-tail nuts while counter-holding the valve body; catch drips in a bucket.

  2. Slack off the long retaining nut with a monobloc spanner, lift the tap clear.

    • Why: Clears the deck for the new fitting with zero sink damage.

    • Pro-tip: Penetrating oil ten minutes beforehand frees rusted threads. 



4. Prepare the mounting surface


  1. Scrape away old putty/silicone, wipe with methylated spirits.

    • Why: A flat, grease-free surface guarantees the gasket seals first time.



5. Assemble the new tap


  1. Screw the flexi tails hand-tight into the mixer body, then nip ¼-turn with a spanner.

  2. Slide the rubber base gasket over the tails.

    • Why: Bench assembly is far easier than inside a cupboard.

    • Pro-tip: A smear of silicone grease on the tail O-rings aids later removal.



6. Seat and align


  1. Feed tails through the sink hole; have a helper hold the tap square.

  2. Fit the rubber then metal horseshoe washer and tighten the retaining nut firmly.

    • Why: Compresses the gasket and locks the body rigidly.

    • Pro-tip: Hand-start the nut to avoid cross-threading in blind space.



7. Connect the supplies


  1. Flush each pipe for a few seconds into a bucket to expel grit.

  2. Attach the hot (left) and cold (right) tails to isolation valves; hand-tight then ½-turn with spanner.

    • Why: Debris-free water protects ceramic cartridges; correct torque prevents crushing the hose liner.



8. Reinstate pressure and test


  1. Open valves slowly; inspect every joint with dry tissue while the mixer runs full-flow for 60 s.

    • Why: Tissue shows even pin-point weeps before cupboards go back.

    • Pro-tip: Leave the base panel off overnight and re-check next morning for peace of mind.



9. Seal the perimeter


  1. Dry the deck; run a fine bead of sanitary silicone where metal meets sink and smooth.

    • Why: Stops capillary water tracking beneath, preventing corrosion marks.



10. Tidy and record


  1. Note valve positions, take a photo of the completed pipework and store with manuals.

    • Why: Speeds any future maintenance or cartridge replacement.




🔍 Completion Checks


  • Tap stands dead-straight; cannot be twisted by hand.

  • Hot flows on left, cold on right; full, even pressure and no aerator splutter.

  • Tissue around every joint stays dry after 10 min at operating pressure.

  • Spout swivels smoothly without sideways play and lever moves freely through its arc.




👷‍♂️ When to call a pro instead


If pipe tails need extensive rerouting, the retaining nut is inaccessible behind stone worktops, or mains pressure imbalance demands pressure-reducing valves, a licensed plumber with specialised monobloc sockets and test gauges can ensure compliance and prevent hidden leaks.

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