Independent comparisons. We may earn from shop links. More info

Under sink instant water heater

Updated: 21 October 2026

The cupboard under the cloakroom basin is empty, the only socket is on the wall beside it, and you want warm water at that one tap. An under sink instant water heater is the tankless box that heats while the tap is open, not a 7 or 10 litre store that heats a jug and then runs out. In this set, several listings say they will sit in that cupboard, and one UK review says the remote stops working once the door hides the case. The rows are on the [main comparison](/hub/hot-water/instantaneous-water-heater-with-remote-control). Who should pay for the Stiebel is on the [best of this set](/hub/hot-water/instantaneous-water-heater-with-remote-control/sub/instantaneous-water-heater-with-remote-control-best).

The cupboard under the cloakroom basin is empty, the only socket is on the wall beside it, and you want warm water at that one tap.

Our top picks

Stiebel Eltron Stiebel Eltron DCE-X 6/8 Premium

Best overall

Stiebel Eltron Stiebel Eltron DCE-X 6/8 Premium
6.9/10about £344.99
View offer
Mulcort Mulcort LF-001 3000 W

Best value

Mulcort Mulcort LF-001 3000 W
5.1/10about £46.99
View offer
YUCHENGTECH YUCHENGTECH 3000 W with remote

Rank 3

YUCHENGTECH YUCHENGTECH 3000 W with remote
5.0/10about £59.89
View offer
On this page
  1. 1.Instantaneous or a few litres stored
  2. 2.Which listings in this set say under the sink
  3. 3.The remote and the closed door
  4. 4.When to stop and buy a store

Instantaneous or a few litres stored

Search under sink instant water heater and the trade results that lead are often small storage heaters. A Heatrae Sadia Streamline page is a 10 litre vented undersink unit at 3 kW, with a heat-up time rather than a flow-through element. It is a stored cylinder, not one of these listings. A stored 7 or 10 litres gives you a proper flow until the jug is empty, then you wait while 3 kW heats the next fill. A tankless 3 kW unit never stores that jug. The temperature falls as you open the tap further or as the winter mains get colder. For a quick hand wash you may prefer the tankless unit. For washing up, the store is the less frustrating machine, and it is outside this set. The buying guide matches kilowatts to a measured jug. Here the decision is which machine belongs in the cupboard.

Which listings in this set say under the sink

Four kept listings claim the cupboard. The Briwellna, at about £108.99, says above or under the sink, including upside down. It is 5.5 kW, with a 40°C maximum and a request for a 25 A double-pole breaker. The YUCHENGTECH at about £59.89 states under the sink at 3000 W, with a remote. UK texts call the fit easy, then say useful warmth needs a trickle. The Mulcort at about £57.99 states under-sink mounting, a remote and a UK plug, and it has no reviews. The Delousiber title says over or under the sink at 6000 W, while UK reviews describe a 13 A style plug and leaks. Do not hide that one in a cupboard. The Stiebel is over-sink. The Mulcort LF-001 does not say under-sink, though one review fitted it in a vanity.
Stiebel Eltron Stiebel Eltron DCE-X 6/8 Premium

Testsieger

Stiebel Eltron Stiebel Eltron DCE-X 6/8 Premium
6.9/10about £344.99
View offer

The remote and the closed door

A handheld remote only moves the buttons. It does not add kilowatts, and it does not see through a chipboard door. On the YUCHENGTECH, a UK review says the remote works when the case is in sight, and is little use once the unit is under the sink. The Mulcort at about £57.99 states a remote that needs two AAA batteries, and the batteries are not in the box. There are no reviews on line of sight. Assume it needs a clear view. Do not buy it because remote appears next to under-sink. The Stiebel’s two memory keys sit on the case, which is why the listing is over-sink. If the only place left is the cupboard, set the heater before you slide it back. A 5.5 kW Briwellna is not a plug-in at all.

When to stop and buy a store

Stop when the job is washing up, a fast fill of a bowl, or two people who will not wait for a trickle. The LF-001 reviews quote instructions around 2.1 litres per minute at 40°C, and about 1.0 litre per minute when the mains is colder. Stop as well when the remote is the feature you cannot give up and the only mount is behind a door. If the basin has to feed a proper wash, leave this set for a stored undersink heater, or mount the Stiebel where you can use the keys.

Common questions

Will a tankless heater fit in a vanity?
Several will, on size alone. The YUCHENGTECH lists a depth of 55 mm, the Mulcort with a remote is about 20 × 11.5 × 7.7 cm, and the Briwellna bullets say about 210 × 172 × 73 mm, including upside down. Fit also means pipe tails, an isolator, and a cable that is not crushed by the trap.
Is a 10 litre under-sink store the same thing?
No. A 10 litre vented heater such as a Heatrae Sadia Streamline stores water and heats it with a 3 kW element, then delivers that water at a normal flow until the store is empty. A tankless heater has no jug to empty. It heats the stream you are drawing, and at 3 kW that stream has to stay small if you want it warm. The trade pages that lead a UK search are usually the store. This comparison is the tankless set.
Can I use the remote with the door shut?
Not on the evidence in this set. A YUCHENGTECH review says the remote needs a direct line of sight and fails once the unit is under the sink. The Mulcort remote needs two AAA batteries that are not included, and nobody has reviewed whether it works through a door. If you shut the cupboard, assume you have lost the handset. Set the temperature before you close the door, or mount the heater where you can see it.
Over-sink or under-sink for the Stiebel?
The listing says over-sink. It does not claim the cupboard. The memory keys and the display are on the case, so you want the case on the wall where you can reach them, close to the tap. UK reviews also say it is not an ordinary socket. Hiding an about £344.99 electronic heater behind a steel bowl wastes the control you paid for and makes the pipe inlets, which owners already call awkward, harder to service.
What if the only socket is on a ring?
Do not treat that socket as the design. A 3 kW heater is already as much as a 13 A plug should carry for a long draw, and the IET has raised the same point for a 3 kW immersion. Anything at 5.5 kW or above needs its own breaker, which the Briwellna bullets put at 25 A. If the ring is all you have, stop and ask an electrician, or choose a small store that is specified for the circuit you actually own.

Related pages

Install an instantaneous water heater

Instantaneous water heater with remote control

Best instantaneous water heater with remote control

What size instantaneous water heater do I need in the UK

Instantaneous water heater for shower use in the UK

Sources

Public UK sources and manufacturer pages named below. amazon.co.uk prices, stars and review counts on these seven listings were read on 20 October 2026. Page updated 21 October 2026.

  1. Stiebel Eltron UK sizing FAQ (retrieved 20 October 2026)
  2. Stiebel Eltron UK, instantaneous versus stored (retrieved 20 October 2026)
  3. Stiebel Eltron UK counter mat (retrieved 20 October 2026)
  4. Stiebel DCE-X 6/8 Premium (retrieved 20 October 2026)
  5. Approved Document P (2013) (retrieved 20 October 2026)
  6. Approved Document G (retrieved 20 October 2026)
  7. IET Wiring Matters, September 2025, 3 kW and a 13 A connection (retrieved 20 October 2026)
  8. Water Fittings Regulations 1999, Schedule 2 paragraph 15 (retrieved 20 October 2026)