Kitchen Taps: Monobloc, Pull-Out Spray, and Instant Hot Water Tap Installation Guide

Kitchen tap replacement is one of the most common plumbing jobs in the UK — quick to quote, quick to complete, and almost always profitable when done right. But taps have changed. Where once a plumber fitted a pair of quarter-turn ball-valve pillar taps in ten minutes, today's kitchen market is dominated by monobloc mixer taps, pull-out spray heads, and increasingly, instant boiling water taps that integrate a mini under-sink boiler. This guide covers the practical trade knowledge you need: tap types, hole sizes, flexible connector specs, isolation, commissioning, and the pitfalls that waste time on the job.

Types of Kitchen Tap

Monobloc Mixer Taps

The monobloc is the standard kitchen tap in new builds and refurbishments alike. It fits through a single 35mm hole in the sink or worktop and has one body housing both hot and cold feeds. A ceramic disc cartridge controls the flow and mix via a single lever or twin handles. Most monobloc taps come with 3/8-inch or 1/2-inch tail connections — always check the spec sheet before ordering flexible connectors.

Key trade points:

• Most monoblocs accept a 35mm hole; some budget ranges require only 32mm. Always measure the existing hole before removing the old tap.
• Ceramic disc cartridges (quarter-turn) are the norm. Failing cartridges are the most common kitchen tap fault — a replacement cartridge is usually £5–15 and a cheaper fix than a new tap.
• Clip-on basin wrenches are essential: under-sink access in kitchens is often obstructed by waste pipework and the back of the cupboard.

Pull-Out and Pull-Down Spray Taps

Pull-out spray taps have a retractable hose fitted to the spout, with a spray/stream toggle on the head. They're popular in fitted kitchens and available at trade price points from brands like KeyPlumb, Bristan, and Grohe. Installation is identical to a standard monobloc, but the hose routing requires care: ensure the hose does not kink or catch on the cabinet structure when extended and retracted.

Most pull-out spray hoses are weighted with a counterbalance — a small magnetic weight inside the cabinet that pulls the spray head back into the spout after use. If the head doesn't retract, the counterweight has usually detached or the hose has snagged.

Bridge (Crosshead) and Traditional Pillar Taps

Pillar taps use two holes at 180mm centres (standard), with individual hot and cold valves. They're still found on older Belfast sinks and in period-style kitchens. Quarter-turn ball-type pillar taps have largely replaced the traditional rubber-washer type at trade level, but you'll still encounter washered taps on service calls. Cartridge replacements, washer packs, and reseating tools remain worth carrying.

Instant Boiling Water Taps

Brands such as Quooker, Zip HydroTap, and InSinkErator Hot 1 combine a boiling water function (98–100°C) with conventional hot and cold mixer functions in a single spout, fed by a pressurised under-sink boiler tank (typically 2–4 litres). Installation scope expands significantly:

• Electrical supply: a fused spur (typically 13A, fused at 5A) is required under the sink. Part P notifiable in England and Wales if the spur is a new circuit extension.
• Cold water supply to the tank: usually 15mm compression or push-fit from the cold supply under the sink, via a dedicated filter cartridge.
• The boiling function is WRAS-approved in all main brands — no separate notification to the water company is required, but check supplier documentation.
• Safety: child lock on the boiling function lever is mandatory per manufacturer spec. Commission and demonstrate to the customer before leaving site.

Hole Sizes and Sink Compatibility

When drilling new holes in stainless steel sinks, use a step drill bit or a hole saw with a bi-metal blade and cutting fluid. Mark the centre carefully — a mis-drilled hole in a stainless sink cannot be repaired. Granite composite sinks require a diamond-tipped hole saw and water cooling; always confirm with the manufacturer that the intended tap will fit before drilling.

Flexible Connectors: Sizing and Specification

Most kitchen monobloc taps are supplied with either 3/8-inch or 1/2-inch tails. The flexible connector must match the tail thread and connect to the supply isolation valve. The standard UK supply pipe under a kitchen sink is 15mm, typically terminating with a 1/2-inch BSP service valve.

Key sizing guide:

• 3/8-inch tap tail → 1/2-inch BSP valve: Use a 3/8" x 1/2" BSP flexible connector (most commonly stocked). These are sometimes labelled 10mm x 15mm.
• 1/2-inch tap tail → 1/2-inch BSP valve: Use a 1/2" x 1/2" BSP flexible (straight or angled as required by the geometry under sink).
• Always use fibred washers (not plain rubber) at both ends — the fibre insert prevents the washer extruding under line pressure.
• Do not overtighten — 1/4 turn past hand-tight is sufficient. Over-tightening cracks the olive or distorts the washer seat.

Flexibles should be replaced at every tap change — reusing old flexibles is false economy. WRAS-approved braided stainless flexibles are the trade standard; avoid chrome-plated brass with plain rubber ends in a kitchen environment where exposure to cleaning chemicals accelerates degradation.

Isolation and Supply

Every kitchen tap supply should be served by a dedicated 15mm isolation valve (service valve, screwdriver-slot type) on both hot and cold. These allow the tap to be serviced without shutting off the house water supply. If there is no isolation valve fitted — common in houses where the original tap was never changed — fit one during the replacement job.

If there is no nearby isolation available (uncommon in a kitchen), close the cold supply at the main stopcock and the hot supply at the service valve on the hot water cylinder or at the boiler's domestic hot water port. Always prove isolation with a residual pressure test before disconnecting.

Supply pipe sizing for kitchen taps: 15mm copper or push-fit is standard for UK domestic kitchens. If the customer reports low pressure at the tap, check:

1. Isolation valve not fully open (common after a previous service)
2. Scale build-up in ceramic cartridge — service or replace the cartridge
3. Flow restrictor in the tap aerator (remove, rinse, refit)
4. PRV set too low — kitchen cold supply at the stopcock may be below 1 bar. See article on pressure reducing valves for diagnosis and adjustment.

Step-by-Step Tap Replacement

Preparation

1. Isolate hot and cold supplies at the service valves under the sink. Confirm isolation by opening the tap — water should stop within a few seconds.
2. Lay a towel in the base of the sink cabinet to catch residual water from the flexibles.
3. Photograph the existing connections before disconnecting — useful if the customer queries the specification of the replacement.

Removing the Old Tap

1. Disconnect the flexible connectors using an adjustable spanner. Have a small container ready to catch water from the tails.
2. Reach up under the sink and undo the back-nut (or back-nut and washers) holding the tap body to the sink. A basin wrench is essential here — clearance is rarely sufficient for a standard spanner.
3. If the back-nut is corroded solid, apply penetrating fluid and wait 10 minutes before re-attempting. Do not use excessive force or you risk cracking the sink deck.
4. Lift the old tap out through the hole. Remove any residual sealant from the hole rim before fitting the new tap.

Fitting the New Tap

1. Fit the plastic seating gasket (supplied with the tap, or use a bead of silicone sealant — check manufacturer preference) to the underside of the tap base.
2. Thread the tap tails down through the sink hole. Have a helper hold the tap in position from above if working alone is impractical.
3. Fit the backing plate, rubber spacer, and back-nut in the order specified by the manufacturer. Tighten the back-nut firmly — the tap should not be able to rotate under normal use — but do not overtighten on ceramic or composite sinks.
4. Connect new flexible connectors: hot to hot tail, cold to cold tail. Tighten to the isolation valves. Do not use PTFE tape on flexible connector joints (compression type) — the fibre washer provides the seal.

Commissioning

1. Open the isolation valves slowly to restore supply. Check for leaks at both ends of the flexibles and at the back-nut/sink deck joint.
2. Run hot and cold through the tap to purge air from the system. Allow 30–60 seconds for any entrained air to clear.
3. If the tap has a flow regulator, set it to the customer's preferred flow rate (usually full flow for a kitchen).
4. For pull-out spray taps: test the hose retraction and check the spray/stream toggle functions correctly.
5. For instant hot water taps: fill the boiler tank per manufacturer instructions, power on the unit, and allow the heating cycle to complete (typically 10–15 minutes) before testing boiling water function. Demonstrate the child-lock operation to the customer.

Common Faults and Diagnosis

Cartridge Replacement

Ceramic disc cartridges are not universal — the diameter, height, spindle direction (clockwise-close or counter-clockwise-close), and port configuration vary between brands. When replacing a cartridge:

1. Note the tap brand and model (often on a label inside the tap box; if unavailable, photograph the cartridge before removal).
2. Remove the handle (usually a grub screw under a push-in cap), unscrew the cartridge retaining nut, and pull the cartridge straight up.
3. Match the replacement cartridge by diameter and height. Inventive Creations, Bristan, and other trade suppliers stock a wide range of compatible cartridges — bring the old one for comparison if the brand is unknown.
4. Fit the new cartridge, aligning the locating tab with the slot in the tap body. Overtightening the retaining nut will crack the cartridge — hand-tight plus a quarter turn is correct.

Water Regulations Considerations

Kitchen taps in the UK must comply with the Water Supply (Water Fittings) Regulations 1999. Key points:

• Backflow protection: A single-check valve (WRAS-approved) should be fitted on the cold supply to a mixing tap to prevent cross-contamination if hot and cold pressures differ significantly. Most WRAS-approved monoblocs have this built into the body — check the product datasheet.
• Fluid Category 2: Standard kitchen taps serving wholesome drinking water are Fluid Category 2 (slight aesthetic contamination risk). No backflow protection beyond a single check valve is required.
• Instant boiling water taps: WRAS-approved models handle the compliance internally. Ensure you specify and fit a WRAS-approved unit.
• Notification: Kitchen tap replacement in an existing location is not notifiable to the water undertaker (it is like-for-like). New supply points require a Section 45/61 notification.

Trade Tips

• Carry a tap body wrench set (Basin Buddy style) — these grip the tap body from above while you tighten the back-nut from below, saving a second pair of hands on most jobs.
• Stock three flexible connector sizes: 3/8" x 1/2" straight, 3/8" x 1/2" angled 90°, and 1/2" x 1/2" straight cover the majority of kitchen tap installations.
• Always replace the aerator on a new-to-customer tap — scale build-up in the old aerator will reduce flow and generate a callback if left in place.
• Take a photo of the waste configuration before starting work — the waste trap position sometimes shifts during access, and customers notice.
• Instant hot tap commissions: Run water through the filter for the manufacturer-specified flush time before first use to remove carbon fines. Always leave the manual with the customer.

Summary

Kitchen tap replacement is a high-margin job when you arrive prepared. The most important trade decisions are: flexible connector sizing to match the tap tail, correct isolation before disconnection, and cartridge-matching for service calls. For instant boiling water taps, electrical supply and filter commissioning extend the scope — price accordingly. Stock the essentials (flexibles, cartridge range, isolation valves, aerators) and most kitchen tap jobs can be completed in under an hour.

Get it from APM Electricals, Acton

We stock what UK trades need — same-day collection from our trade counter in Acton. No minimum order. Trade accounts welcome.

Browse our water heater range, or visit us at 24 Western Avenue, Acton, London W3 7TZ. Call 020 8702 8080 to check stock.