Boiling water tap installation: what to expect and what it costs

What the job involves

A boiling water tap installation has two halves: plumbing and electrics. The plumber isolates the cold supply, fits the insulated tank inside the under-sink cabinet, mounts the tap in the existing or a new tap hole, and connects the tank to the water supply and the tap. On a 4-in-1 they also fit the filter housing and connect the cartridge. For a straightforward like-for-like swap, that is a few hours of work.

The part people overlook is the socket. The tank needs its own correctly earthed 13 amp socket inside the cabinet. If you already have one, you are in the cheap lane. If you do not, an electrician has to add one, and in England and Wales that is notifiable work under Part P of the building regulations. That single factor is the biggest swing in the price.

What it costs

These are typical ranges, not quotes. Hard-water areas with limescaled existing pipework can push the figure higher, because more of the old fittings need replacing. Get a figure for your own job, including a soft-water-area adjustment, with the installation cost estimator, and see typical costs and water hardness for your city on the installers page.

Choosing the right tank size for your cabinet

Before the plumber arrives, measure your under-sink space with the waste pipe and any existing units in mind. Tanks range from compact 2 litre units that tuck into a corner to 7 litre tanks that need a clear run of cupboard. A bigger tank pours more before it reheats, which suits a heavy-use family, but it eats storage and costs slightly more to run. Most households are well served by a 2.4 to 4 litre tank. If the cabinet is shallow or already crowded with a waste disposal or water softener, flag that when you order, because it narrows your model choice. Every model page lists the tank dimensions.

How long it takes

A like-for-like swap with the socket already in place is usually a morning's work, often under two hours. Add an hour or two if the tap hole needs adapting or the cabinet needs cutting for the tank. The slow path is the electrical work: if a new socket is needed, the electrician's visit may be a separate appointment, so the whole job can spread across two days even though the hands-on time is short. Booking the plumber and electrician for the same window, where possible, keeps it to a single day.

Why you should not DIY it

Some confident DIYers fit the plumbing themselves, but the electrical side is the issue. Adding or moving a socket is notifiable work, getting it wrong is a genuine safety risk, and most manufacturers require professional installation for the guarantee to stand. The sensible split is to buy the tap yourself, then have a qualified plumber fit it and an electrician add the socket if one is needed.

> The tap is the cheap mistake to make twice. The socket and the tank seals are not. Pay once for a proper fit and keep the warranty intact.

Renting versus owning

If you own your home, a boiling tap is a straightforward upgrade and the install cost is yours to recover through daily use. If you rent, treat it as a conversation with your landlord first. The install alters the plumbing and the electrics, both of which usually need permission, and a removable design like a flexible-hose model is easier to reverse at the end of a tenancy. Without the landlord's agreement, a kettle remains the practical choice.

How to prepare

A little preparation keeps the cost at the low end:

• Check for an existing under-sink socket. Its presence or absence sets your price bracket more than anything else.
• Confirm your tap hole. A single-lever mixer hole usually accepts a boiling tap; a twin-tap arrangement may need adapting.
• Measure the cabinet. Match the tank size to the space and to how much water you draw at once.
• Know your water hardness. Above 200 mg/l you should plan for filtration and more frequent descaling from day one. Check your city on the installers page.

Once it is in, the only ongoing jobs are filter changes on a 4-in-1 and occasional descaling, both covered in our maintenance and descaling guide. To choose the model itself, start with the best boiling water taps round-up.