Boiling water taps: the tank under the sink, electrics and limescale

How boiling and hot water kitchen taps work in UK homes, what goes in the cupboard under the sink, why the electrical supply is work for a qualified electrician, what Water Regs UK's guidance says about these taps, and how hard water and filters affect them.

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A boiling water tap gives near-boiling water on demand at the kitchen sink, so you do not need to boil a kettle. Some are a separate small tap. Many are 3-in-1 or 4-in-1 taps that combine normal hot and cold with boiling water, and sometimes filtered cold or chilled water. Quooker made the idea well known in the UK; many other brands now sell them.

This guide explains what is involved in having one, where the plumbing and electrics come in, and what to think about in a hard water area. It is not an installation guide.

What goes under the sink

A boiling water tap is really a small water heater plus a special tap. Under the sink there is usually:

a tank (often called the boiler or heater) that stores a small amount of water and keeps it hot;
a filter cartridge on many models, to reduce scale and improve taste;
flexible hoses linking the tank to the tap and to the cold supply;
a pressure-limiting or safety valve arrangement set by the maker;
a plug or electrical connection for the tank.

Some taps have no stored tank and heat instantly instead. Either way, measure the cupboard before you buy. The tank and filter take up a lot of the space under a sink, and they need room for servicing and filter changes. A waste disposal unit or a dishwasher connection may be competing for the same space.

What Water Regs UK says

Water Regs UK publishes technical guidance on multifunction taps (September 2022). It is non-statutory guidance, but it sets out how the water fittings regulations apply. In plain terms, it says:

for its purposes, boiling water taps with storage of any capacity are treated as unvented water heaters, and those without storage as instantaneous water heaters;
a boiling water tap installation is treated as a secondary hot water system;
the tap system must have adequate devices to prevent contamination by backflow;
safety device discharges must be safe and conspicuous, and should be visible and not continuous;
suitability includes installation, operation and maintenance in accordance with the manufacturer's instructions;
satisfying the water fittings regulations does not automatically mean all Building Regulations requirements are met.

Water Regs UK's drinking water taps page adds that if installing a multifunction tap is notifiable, advice should come through the notification process, and if it is not, the owner or occupier still has a legal obligation to make sure the plumbing complies. If you are unsure, ask your water supplier or use a plumber who knows the water regulations.

The same page says a drinking water tap should, where possible, be supplied direct from the mains rather than through a fitting that stores, treats or filters the water. Ask how the tap you are looking at supplies ordinary cold drinking water.

The electrical connection

The tank needs power, usually from a socket or supply in the cupboard in the position the maker's instructions show. Many kitchens do not have one in the right place.

Adding or moving a socket or supply under the sink is electrical work for a qualified electrician. A kitchen sink cupboard puts water and electrics close together, and in England Part P of the Building Regulations covers electrical safety in homes. See the Approved Document P page on GOV.UK and ask your electrician what applies. We do not give wiring instructions.

Book the electrician before the plumber fits the tap, so the supply is ready and in the position the tap maker's instructions show.

The plumbing side

The tap needs:

a cold mains supply at a pressure the maker says suits the tank. Some boiling taps are made for higher-pressure systems only, so check the specification against your supply;
for 3-in-1 or 4-in-1 taps, a hot supply as well;
isolation valves on each supply so the tap can be serviced without shutting off the house. See isolation valves;
a tap hole in the sink or worktop of the right size.

Fitting the tap itself is similar to fitting any kitchen mixer, which our kitchen sink installs guide covers. The tank, safety valve and any connection to the waste must follow the maker's instructions exactly. If the tank leaks, turn off its isolation valve and switch it off at the power supply before calling the installer.

Scale and hard water

Heating water drives limescale out of it. In a hard water area a boiling water tank can scale up, which may slow it down, make it noisier or shorten its life. Our guides to limescale and water quality and hard water areas explain what hardness means for your home.

Ways makers deal with it:

a scale-reducing filter cartridge, changed at the interval the maker says. Hard water usually means more frequent changes;
a descaling routine in the user manual for some models;
a water softener on the house supply, if the tap maker approves softened water for the tank. Some do; some do not. Check before you rely on it. Our water softeners guide explains the kitchen tap question.

Keep a note of the filter type and when you last changed it.

Safety in use

Boiling water can scald quickly. Most taps have a child-resistant handle or a button that needs pressing and turning. Show everyone in the house how it works, keep the spout clear of hands and consider where the tap sits if young children or vulnerable people use the kitchen.

Example tap at Wickes

We haven't tested this. It is an example, with what the retailer's page says.

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Abode Prothia 3-in-1 hot water kitchen tap, chrome. Wickes lists a 2L stainless steel tank, a scale inhibiting filter cartridge, an insulated swivel spout and a slide and twist safety lock on the hot handle. Wickes also lists it for use with high pressure systems, so check your supply first. The electrical supply in the cupboard is work for a qualified electrician, and the tank should be fitted as the maker's instructions say.

View the Abode Prothia 3-in-1 tap at Wickes

Do boiling water taps need an electrician?

The tank needs an electrical supply under the sink. If there is no suitable socket or supply there already, adding one is work for a qualified electrician, and Part P applies in England.

Do boiling water taps work in hard water areas?

Yes, but scale builds up faster. Use the maker's filter, change it at the interval they set, and check whether the maker approves softened water before relying on a softener.

Do I need to tell the water company about a boiling water tap?

It may be notifiable depending on the installation. Water Regs UK says that if it is not notifiable, the owner or occupier still has a legal obligation to make sure the plumbing complies. Ask your water supplier or installer.