Best tankless water heater UK
Updated: 17.10.2026
The best tankless water heater is not the model with the highest star rating. You need a heater that matches one outlet, the available electrical supply and the flow you expect on a cold day. From the seven amazon.co.uk listings in our [tankless water heater comparison](/hub/hot-water/tankless-water-heater), the Stiebel Eltron DCE-X 10/12 is the top pick when a suitable high-current circuit is possible and the job is a basin or a compatible shower, not a bath. For a remote hand-wash basin, the ThermoMate ET055 is the lower-cost option. The conditions matter more than the badge. A qualifying purchase can earn a commission at no extra cost to you.
The best tankless water heater is not the model with the highest star rating. You need a heater that matches one outlet, the available electrical supply and the flow you expect on a cold day.
The best tankless water heater is not the model with the highest star rating. You need a heater that matches one outlet, the available electrical supply and the flow you expect on a cold day. From the seven amazon.co.uk listings in our tankless water heater comparison, the Stiebel Eltron DCE-X 10/12 is the top pick when a suitable high-current circuit is possible and the job is a basin or a compatible shower, not a bath. For a remote hand-wash basin, the ThermoMate ET055 is the lower-cost option. The conditions matter more than the badge. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Power | UK reviews | Stated flow | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Stiebel Eltron Stiebel Eltron DCE-X 10/12 | 12 kW | 4.4 from 116 | 5 L/min | 8.8 | about £412.86 | View offer |
| Preis-Tipp |  ThermoMate ThermoMate ET055 5.5 kW | 5.5 kW | 4.0 from 248 | 3 L/min | 8.0 | about £109.74 | View offer |
| Alternative |  TopSer TopSer BS-18DC-3 Pro tap | 3 kW | 4.0 from 88 | 3 L/min | 8.0 | about £49.99 | View offer |
On this page
Top pick when the circuit can take it
The Stiebel Eltron DCE-X 10/12 combines more power with electronic control. Its amazon.co.uk listing gives 12 kW, 5 litres per minute, a maximum of 55°C and a price of £412.86, with 4.4 stars from 116 reviews, energy class A and a two-year warranty line.
UK buyers describe stable hot water at basins and some successful shower installations, provided the electrical supply is adequate. Reviews also say it is not suitable for filling a bath, and at least one kitchen mixer suffered poor flow. The 5 L/min line is the listing figure, not a measurement we made.
The circuit is the condition. Stiebel's technical data for this model class gives roughly 47.8 or 57.0 A at 230 V, with 50 or 60 A protection in the datasheet. Those figures need a professional reading for the property. They are not a DIY wiring recipe. If the home cannot support that work, this is not the right buy. The tankless heater buying guide is the check before you order.
Best value for a cloakroom basin
The ThermoMate ET055 is the best value for hand washing at a remote sink. It costs £109.74 on the amazon.co.uk listing and has 4.0 stars from 248 reviews, the largest review count in this set. The title states 5.5 kW with no plug, and the product bullet calls for 25 A or higher. That is a more coherent starting point than a nominal 6 kW heater supplied with a regular plug.
Useful performance is still modest. The capacity field says 3 litres per minute, but UK reviewers include reports of around 1 litre per minute when the water is actually warm. Buyers who like it use it for a cloakroom draw of less than a minute, not a large bowl or a conventional shower.
The table prints a 25°C maximum while reviewers report warmer water, and the two pressure figures disagree. The data plate and the manual have to settle that.
What not to treat as a bargain
The Delousiber RY-LZT-4 shows why price per kilowatt is a poor measure. At £46.99 it claims 6 kW and a temperature range up to 55°C. Its bullet asks for a dedicated circuit and a fuse of at least 40 A, yet reviewers report that a normal plug is fitted. A standard UK 13 A socket cannot supply a genuine 6 kW load, so the conflict has to be resolved before installation.
The listing shows 3.1 stars from 20 reviews, with repeated reports of leaks, blown fuses and units failing within days or weeks. One buyer reported about 50°C after six weeks. That case does not cancel the electrical conflict. This is not the value pick.
The £44.99 laloohome and the £55.99 Mulcort UK-plug listing have no UK reviews in this set. The laloohome page disagrees with itself about 6000 W or 5500 W, and the Mulcort box contents differ between two lines. A low price does not replace a confirmed plug or a review record.
Point-of-use picks, not a whole-house system
One modest shower under stated conditions is not a high-power electric shower or a stored system. Measure the litres per minute and read the kilowatts, flow and temperature guide. If the sum only works as a trickle, the tankless model is the wrong type.
For a kitchen bowl on a modest circuit, compare instantaneous and storage water heaters. A small store uses cupboard space and loses some heat while waiting, but it can release a useful volume faster than a 3 kW instant unit and then reheat. The recommendation stays conditional: Stiebel where the electrics and the point-of-use demand fit, ThermoMate for restricted hand washing, and storage or another system when the job falls outside both.
Common questions
Which tankless heater is the top pick in this set?
The Stiebel Eltron DCE-X 10/12 is the top pick because it combines 10/12 kW-class output, electronic temperature control and the strongest review score in this set. Choose it only if a professional confirms the high-current circuit and you need basin or compatible shower service rather than bath filling.
Who should not buy the Stiebel?
Skip it if you need a 13 A socket, want to fill a bath, cannot justify a new circuit, or expect several outlets at normal flow at the same time. The £412.86 listing price is only part of the cost. Installation may be substantial, and the stated 5 L/min still depends on inlet and target temperatures.
What is the cheaper choice for a cloakroom?
The ThermoMate ET055 is the best-value hand-wash option at £109.74. Its 5.5 kW rating and review base make it more credible than sparse-review 6 kW bargains, but feedback suggests warm flow may fall to roughly 1 litre per minute. It is not the shower or kitchen-bowl recommendation.
Is the highest star rating automatically the winner?
No. Ratings describe buyer experience across installations that may differ from yours. A heater with strong reviews is still unsuitable if its current demand exceeds your circuit or its flow misses the outlet. Rating, review count, specification coherence, controls, price and repeated complaints belong together.
Will a 6 kW heater work from a normal plug?
Not as a genuine 6 kW load on a standard UK 13 A socket. If a listing combines those claims, stop and verify the delivered data plate and manual with a competent electrician. Do not assume the plug proves the wattage is safe, or that the advertised output will be available.
Related pages
Sources
Public UK sources used for this comparison, last checked on 17 October 2026.
- Approved Document G (2024 amendments) (retrieved 17.10.2026)
- Approved Document P (retrieved 17.10.2026)
- IET Part P frequently asked questions (retrieved 17.10.2026)
- HSE HSG274 Part 2 (retrieved 17.10.2026)
- Hyco instantaneous water heater chart (retrieved 17.10.2026)
- Stiebel Eltron: what size instantaneous water heater do I need? (retrieved 17.10.2026)
- Stiebel Eltron: instantaneous versus stored water heaters (retrieved 17.10.2026)
- Stiebel Eltron DCE-X 10/12 technical data (retrieved 17.10.2026)
- amazon.co.uk listings for the seven ASINs in this comparison (retrieved 17.10.2026)