How to Install a Boiling Water Tap

Summary

Boiling water taps have gone from a rare high-end fitting to a mainstream kitchen upgrade over the last several years, and they're now a common line item on kitchen refurbishment quotes. The installation sits across two trades — plumbing (cold water connection, tap fitting, drainage for the tank's overflow/drip tray) and electrical (dedicated spur, RCD protection) — and a competent kitchen fitter or plumber can usually complete the plumbing side, but the electrical connection needs to be carried out or signed off by someone competent to certify it under Part P.

The tank itself — a small, well-insulated unit that heats and stores water at or close to 100°C — sits in the cabinet beneath the sink or in an adjacent cabinet if under-sink space is tight (extended supply lines are available from most manufacturers for this purpose). Getting the tank's position right matters for both practical access (filter changes, annual descaling in hard-water areas) and safety (adequate ventilation, stable mounting, kept clear of other stored items that could be damaged by heat or accidentally trap moisture against the tank).

The most common installation mistakes are not plumbing or electrical faults but positioning ones: mounting the tank where the filter can't be reached without emptying the cabinet, running the cold feed without isolation and a proper WRAS-approved connection, and under-specifying the electrical circuit for the specific model being fitted — tank wattage and recommended circuit protection vary meaningfully between manufacturers and models, and the manufacturer's installation instructions for the specific unit are the authoritative source, not a generic assumption based on a different brand.

Key Facts

• Tank type — most boiling water taps use a small, insulated, low-volume tank (commonly in the low single-digit litres, model-dependent) that heats water to near 100°C and stores it ready for instant draw, distinct from a full hot water cylinder.
• Water connection — cold mains feed via a dedicated isolation valve (a T-piece off the existing kitchen cold supply, or a separate feed), through the manufacturer-supplied inline filter, into the tank.
• WRAS approval — all fittings in contact with the potable water supply, including the tap, filter housing and any flexible connectors, must be WRAS-approved under the Water Supply (Water Fittings) Regulations 1999.
• Isolation valve — a dedicated isolation valve should be fitted on the cold feed to the tank, separate from (or in addition to) the main kitchen sink isolation valves, so the unit can be isolated for filter changes or servicing without shutting down the whole kitchen cold supply.
• Filter replacement — inline filters typically need replacing on a fixed cycle (commonly every 6 months, model-dependent) or sooner in hard-water areas — always check the specific manufacturer's guidance rather than assuming a universal interval.
• Electrical supply — a dedicated fused spur is required, typically 13A (fused connection unit) or sometimes 16A/20A depending on the tank's power draw — confirm against the specific model's installation manual rather than assuming a standard 13A fused spur always suffices.
• RCD protection — the spur circuit should be RCD-protected; kitchens are not a BS 7671 "special location" in the same way bathrooms are (Section 701), but socket-outlets and fixed appliances in a kitchen still commonly fall under the general RCD protection requirements of BS 7671:2018+A2:2022 for the circuit type involved.
• Part P notification — new circuits or fused spurs installed in a kitchen are notifiable electrical work under Approved Document P; work should be carried out or certified by a competent person scheme member (NICEIC, NAPIT, ELECSA) or notified to Building Control.
• Drainage/overflow — most tanks have a small drip tray or overflow outlet beneath the tap body at the sink deck; this typically drains via a small tube routed into the sink waste trap, not a separate drainage connection — check the specific model's installation guide for the drip tray drainage method.
• Mounting location — the tank must be mounted upright (per manufacturer instruction — orientation matters for the internal heating and pressure-relief mechanism), on a stable, level surface or bracket, with clearance for ventilation and for the filter/tank to be accessed for servicing.
• Cabinet ventilation — avoid fully sealing the tank into an airtight compartment; residual heat and any minor condensation need somewhere to dissipate, and manufacturers generally specify a minimum clearance around the tank body.
• Tap hole size — boiling water taps typically need a single tap hole in the worktop or sink, though 3-in-1 and 4-in-1 models (boiling, cold filtered, and sometimes hot/sparkling) may need a slightly larger bore — check the model's worktop cutout template before cutting.
• Combining with a standard mixer tap — many installations retain the existing kitchen mixer tap alongside a separate boiling water tap in an adjacent tap hole, rather than replacing the mixer — confirm with the customer whether a 2-tap-hole sink/worktop is available or whether an additional hole needs cutting.
• Cutting an additional tap hole in worktops — laminate worktops can be drilled/cut on site; stone (granite, quartz) worktops generally need the additional hole cut by the fabricator before or during template/fitting, not on site after installation — plan this into the kitchen fitting sequence, not as an afterthought once the boiling tap arrives.
• Water pressure requirements — most models have a minimum and maximum operating pressure range specified by the manufacturer; very high mains pressure may need a pressure-reducing valve, and very low pressure sites should be checked against the specific model's minimum before quoting.
• Servicing — annual servicing (descaling, tank check, filter change per schedule) is recommended, more frequently in hard-water areas; flag this to the customer as an ongoing cost at quote stage, not a one-off installation.

Quick Reference Table

Detailed Guidance

Planning the installation before the kitchen fit-out is finished

Boiling water taps are far easier to install cleanly when planned into the kitchen design before worktops are templated and cabinets are fitted, rather than retrofitted afterward. Key decisions to make early:

• Which cabinet will house the tank — usually the sink cabinet, but an adjacent cabinet is an option if under-sink space is needed for a waste bin, filtration unit, or other equipment, using the manufacturer's extended connection kit
• Whether the tap will sit alongside the existing mixer tap (two tap holes) or replace it, and whether that decision affects the worktop/sink specification ordered
• Confirming with the worktop fabricator (for stone worktops) that the additional tap hole is included at template stage

Cold water connection

1. Isolate the mains cold supply to the kitchen before starting work.
2. Identify a suitable take-off point on the existing cold feed — typically a T-piece connection using a WRAS-approved fitting.
3. Fit a dedicated isolation valve on the new branch feeding the tank, positioned so it remains accessible after the cabinet is fully fitted out (not buried behind stored items).
4. Fit the manufacturer-supplied inline filter in the position and orientation specified in the installation manual — filters are typically directional and must be fitted the correct way round for flow.
5. Connect the filtered supply to the tank inlet using the manufacturer's supplied fittings — do not substitute generic flexible hoses unless confirmed WRAS-approved and compatible with the tank's connection type.
6. Check the mains pressure against the manufacturer's minimum/maximum operating range before completing the connection — fit a pressure-reducing valve upstream if the supply exceeds the tank's maximum rated pressure.

Tank mounting

1. Choose a stable, level base or use the manufacturer's mounting bracket — most tanks are designed to stand upright on the cabinet floor or be wall/side-panel mounted via a bracket, depending on model.
2. Position the tank to leave clear access to the filter and any manual reset or descale points, without needing to remove the tank or empty the whole cabinet to service it.
3. Maintain the manufacturer's specified minimum clearance around the tank for ventilation — do not pack the tank tightly against cabinet walls, bin units, or plumbing pipework insulation.
4. Route the outlet pipe from tank to tap without kinks or tight bends that could restrict flow or strain the connection over time.

Fitting the tap

1. Cut or confirm the tap hole per the manufacturer's template (single hole for a standalone boiling tap, or check the specific bore size for 3-in-1/4-in-1 combination models).
2. Fit the tap body through the worktop/sink deck with the manufacturer's supplied seal, washer and fixing nut, following the same basic principle as any kitchen tap installation (see kitchen sink installation).
3. Connect the tap's outlet line down to the tank, and the drip tray drainage tube (if fitted) to the sink waste trap or as specified by the manufacturer.
4. Tighten and check for leaks at every joint before restoring water supply — pressure-test the connection by running the tap through its full range (cold, filtered cold, boiling) once commissioned.

Electrical connection

1. Confirm the tank's power rating and the manufacturer's specified circuit protection (commonly a 13A fused spur, though some models specify differently) — do not assume without checking the specific installation manual.
2. Run a dedicated spur from an appropriate point on the ring or radial circuit, or from the consumer unit directly, per BS 7671:2018+A2:2022 — this is notifiable work under Part P and should be carried out or signed off by a competent person.
3. Fit a fused connection unit (FCU) with a clearly visible isolating switch, positioned so the tank can be electrically isolated for servicing without accessing the consumer unit.
4. Confirm RCD protection is present on the circuit.
5. Test and certify the new circuit — issue a Minor Works Certificate (or Electrical Installation Certificate if part of a larger rewire) and notify via a competent person scheme or Building Control as appropriate.

Commissioning

1. Fill and prime the tank per the manufacturer's start-up procedure — most tanks require a specific fill sequence before first power-up to avoid the heating element running dry.
2. Check for leaks at every joint under full system pressure and during a full boiling-draw cycle.
3. Set the tap's safety features per manufacturer instruction (many models have a child-lock or twist-and-press mechanism for the boiling function — confirm this is demonstrated to the customer at handover).
4. Demonstrate filter location and replacement process to the customer, and note the recommended replacement interval and any manufacturer app or reminder system.

Servicing and aftercare — set expectations at quote stage

Unlike a standard mixer tap, a boiling water tap has an ongoing maintenance requirement: periodic filter replacement (typically every 6 months, sooner in hard-water areas) and recommended annual servicing/descaling, particularly in hard-water regions where scale build-up inside the tank reduces efficiency and can eventually affect the heating element's lifespan. Flag this clearly to the customer at quote stage as an ongoing cost, separate from the installation price — it's a common source of customer surprise if left unmentioned.

Frequently Asked Questions

Does a boiling water tap need building control approval like an unvented hot water cylinder?

Generally no — most boiling water tap tanks store a very small volume of water, well below the 15-litre threshold that triggers Approved Document G3 unvented hot water storage system requirements (which apply to systems like unvented cylinders). Always check the specific tank's stated storage capacity in the manufacturer's technical data before assuming this exemption applies, since capacities vary by model and manufacturer.

Can I fit a boiling water tap on a plug-in socket instead of a hardwired spur?

Most manufacturers specify a dedicated fused spur (hardwired connection) rather than a plug-and-socket connection, partly because the unit is intended to be a fixed, permanently connected appliance rather than something regularly unplugged, and partly to ensure the correct fuse rating is dedicated to that circuit. Check the specific model's installation manual, but a hardwired spur installed to Part P is the standard approach.

What water pressure do I need for a boiling water tap?

This varies by manufacturer and model — always check the specific unit's minimum and maximum operating pressure in the installation manual. Very low-pressure systems (some older gravity-fed properties) may fall below a model's minimum requirement, in which case a booster pump may be needed upstream; very high mains pressure may require a pressure-reducing valve to bring it within the tank's rated maximum.

Can I install a boiling water tap myself as a competent DIYer, or does it need a professional?

The plumbing connection is broadly similar in skill level to fitting any kitchen tap and can be within reach of a competent DIYer, but the electrical spur is notifiable work under Part P and should be carried out by, or certified by, a person competent to do so — either a registered competent person (NICEIC, NAPIT, ELECSA) or via Building Control notification. Most manufacturers also specify that installation by an unqualified installer may affect the product warranty, so check the specific terms before assuming DIY installation is warranty-safe.

Regulations & Standards

• Water Supply (Water Fittings) Regulations 1999 — requires WRAS-approved fittings for all components in contact with potable water, including the tap, filter and connecting fittings.

• Building Regulations Approved Document G — sanitation, hot water safety and water efficiency; G3 unvented hot water storage requirements generally do not apply to low-volume boiling water tap tanks below the 15-litre threshold, but confirm per model.

• Approved Document P — electrical safety in dwellings; the dedicated fused spur for a boiling water tap is notifiable electrical work.

• BS 7671:2018+A2:2022 — Wiring Regulations (IET Wiring Regulations); governs the electrical installation, circuit protection and RCD requirements for the spur.

• WRAS Water Regulations Guide — comprehensive guide to compliant plumbing installations and approved fittings.

• WRAS: Water Fittings and Materials Directory — search approved fittings for boiling water tap components

• Approved Document G — official guidance on hot water storage and water efficiency

• Approved Document P — Part P electrical safety notification guidance

• NICEIC — Competent Person Scheme — electrical certification and notification for domestic work

• kitchen sink installation — general kitchen sink and tap installation, WRAS fittings, isolation valve and waste connection guidance

• kitchen plumbing — kitchen plumbing general guidance

• kitchen electrics — kitchen electrical circuit planning and appliance spurs

• stopcock types — isolation valve types and specification for the cold feed connection