The best tankless water heaters 3.5kW, compared.
Top pick: Axelrivet 3.0 kW under-sink Best value: Axelrivet 3.0 kW under-sink – At about £44.99 it states 3,000 W, a flow and a one-year warranty, and it averages 3.1 from 5 reviews. It is the stronger of the two £44.99 units, and it is not a 3.5 kW heater. Updated 17.10.2026.
A 3.5 kW tankless water heater is a small electric instantaneous heater with no cylinder. It is for one hand basin, or a very small sink, close to the tap. You judge it by the watts in the technical details, and by whether the circuit can supply 15.2 A at 230 V. A BS 1363 plug covers appliances not above 13 A, so a true 3.5 kW load sits outside that plug. Fourteen reviews average 2.2 stars, and some buyers report water around 18–30°C. The rise formula and the circuit rules are in the [3.5 kW tankless buying guide](/hub/hot-water/tankless-water-heater-3-5kw/sub/tankless-water-heater-3-5kw-buying-guide). People also buy one to replace a long draw-off from a distant cylinder, still for a basin only. A shopper who wants a shower is in the wrong category.
A 3.5 kW tankless water heater is a small electric instantaneous heater with no cylinder. It is for one hand basin, or a very small sink, close to the tap.
18 products checked · 56 hrs invested · +18,600 readers
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Personal buying guide
Question 1 of 2
Where will you use it?
The Axelrivet YWW-RSQX-01 is listed at 3,000 W and £44.99, so it is the next power down from 3.5 kW rather than the same heater. The title says UK Plug, a bullet says 2.9 L/min and 30–55°C, and a separate spec field prints 131°F and 2.9 litres, which is not the same statement. Five amazon.co.uk reviews average 3.1 stars, on a printed one-year warranty and a 20 cm by 23.5 cm body weighing 1.25 kg. lynne says it works after a difficult setup, and Mark Dyson describes an under-sink fit. john davies says it died after about 10 seconds and then gave cold water only, on a socket that was still live. Lucas says it heated only at very low pressure, enough for a small basin, and that a meter showed about 4,200 W against the 3,000 W listing. At 230 V, 3,000 W is about 13.0 A, but that higher reading is a reason not to treat the title plug as a finished circuit.
Pros
Cons
Best for: A small basin if you want the 3.0 kW neighbour at £44.99 and can accept a five-review sample.
Less suitable: A stated 3,500 W element, a kitchen tap opened fully, or a shower.
Specifications
Common questions
Is this a 3.5 kW heater?
No. The title and the heat-output field say 3000 W. One review says the unit drew about 4200 W.
Does the listing include a UK plug?
The title says UK Plug. The spec table does not name BS 1363.
What flow does the listing claim?
A bullet says 2.9 L/min and 30–55 C. A separate capacity field says 2.9 litres. Both strings are printed.
The Builrand ZXK0410 lists 3,000 W and a 50°C maximum at £44.99, in an 11 cm by 19 cm body that weighs 1 kg, with an LED display and brass given as the material. Eight amazon.co.uk reviews average 2.7 stars, and the five review texts on the listing do not add up to a repeated praise theme. Lukasz and Andrew Mulkerrins report no useful heat, patrick ohara reports a leak from the bottom, and Sanaz beyk returned the unit. Mrs G Rowles says it misses the stated temperature and is not fit for purpose, while noting that a low temperature can suit young children. The title says 220 V and IPX4, and the spec block does not repeat either line. A bullet promises tool-free setup and, in the same line, professional installation for UK plumbing. It is a compact 3.0 kW basin unit with a thin, mostly negative sample, not a 3.5 kW heater.
Pros
Cons
Best for: A tight cupboard under one basin, only if you accept the heat and leak reports first.
Less suitable: A stated 3,500 W heater, dish washing, or any spot where a leak would meet the electrics.
Specifications
Common questions
Is this a 3.5 kW heater?
No. The heat-output field says 3000 W. The title says 220V and IPX4.
What do the reviews say about heat?
The listing average is 2.7 from 8 reviews. Review texts on the listing say there is little or no heat, and one says it leaks from the bottom.
Does the listing say installation is tool-free?
A bullet says tool-free setup and, in the same bullet, recommends professional installation for UK plumbing standards.
The MRNIU MRNIU-55A is the only unit in this set whose technical details state 3,500 W and 230 V, with a listed flow of 4 L/min, a 55°C maximum and a 6 bar limit. At £42.00 it is the lowest shelf price here, in a 26 cm by 19 cm body weighing 1.4 kg, and the box lists a remote. Fourteen amazon.co.uk reviews average 2.2 stars. Rich M, gosia and Nolene report water around 18°C, 27°C or 30°C with the control at 55°C, and gosia could not wash dishes. Shelley found it warm enough for hand washing in about 5–10 seconds once the flow was reduced, and says it is not a shower, which matches the listing. Shelley and Rose report a three-pin plug that the spec table does not mention, on a load of about 15.2 A. Instructions drew complaints, and one unclear review says the unit did not heat. The review sample is still small, and none of these temperatures was measured in a lab.
Pros
Cons
Best for: One basin for hand washing, with the flow kept low and a supply designed for about 15 A.
Less suitable: Washing up, a shower or a bath, or a 13 A plug used as the supply.
Specifications
Common questions
Does the listing say this is for a shower?
No. The listing says it is for kitchen sinks, wash basins and utility sinks, and not for showers, bathtubs or whole-house hot water.
What power is in the spec table?
3500 W and 230 V. The title also says 220V.
Does the spec table list a 13 A plug?
No. Reviews from Shelley and Rose say a three-pin plug was fitted. That is a review report, not a spec line.
This Generic listing, B0G64LCBWG, is priced at £52.99 and titled as a 3.5 kW compact electric shower, but the technical details do not state wattage, voltage, flow, size or weight. There is no customer-review line and no review text, so there is no star average to weigh. Bullets mention a rotary dial from 30°C to 60°C, an LED display and IPX4, and none of that is copied into the technical-details block. Amazon questions on bathroom use, a safety shut-off and minimum water pressure have no answer on the listing. The image URL is the same as ASIN B0H8Q2SG5H, which is listed at a different price. The date available is given as 10 December 2025. A shower title without watts in the spec table is not evidence that the unit will run a UK cubicle.
Pros
Cons
Best for: Checking how thin a 3.5 kW title can be before you leave the listing.
Less suitable: Ordering a basin heater or a shower from this page as it stands.
Specifications
Common questions
What wattage is in the technical details?
None. The title says 3.5 kW. The technical details block does not state wattage, voltage or flow.
Is there an Amazon review count?
No. The listing has no customer-review line and no review texts.
Does the listing state a minimum water pressure?
No. An Amazon question asks for it. The listing has no answer and no pressure figure.
Model A-1, part number KM-3c8rCX, is titled as a 3.5 kW electric shower and priced at £60.99, with China given as the country of origin. The technical details do not state wattage, voltage, flow or dimensions, and the listing has no customer-review line. Bullets mention a 30–60°C rotary dial, an LED display and IPX4 without placing those figures in a spec table. The image URL matches B0G64LCBWG, listed at £52.99, so the extra £8.00 does not add a wattage line or a review. There is no Best Sellers Rank on the listing, and nothing here lets you size a circuit or a tap. Indoor and outdoor shower wording in the bullets is a claim, not a use anyone has reviewed.
Pros
Cons
Best for: A comparison point against a listing that prints 3,500 W in the technical details.
Less suitable: Paying the higher of the two title-only prices, or fitting it as a shower.
Specifications
Common questions
What wattage is in the technical details?
None. The title says 3.5 kW. The technical details do not state wattage, voltage or flow.
Is this the same listing as B0G64LCBWG?
No. It is a different ASIN and price. The listings use the same image URL.
Is there an Amazon review count?
No. The listing has no customer-review line and no review texts.
Five amazon.co.uk listings are scored out of 100. The comparison uses five shares: specification 30, basin fit 20, stars 20, review count 10 and price 10. Rounded so the weights below sum to 100, they are 33, 22, 22, 11 and 12. The product score is that total after deductions, capped at 100. There is no laboratory test. Lukewarm reviews, a reported three-pin plug on about 15.2 A, little or no heat, a leak, heat only at a trickle with a higher watt reading, and a stop after about 10 seconds are taken off.
Specification in the technical details
33%Wattage, voltage, flow, one maximum temperature, and size or pressure in the spec table. A conflicting second temperature scores less. A title with no spec line scores nothing here.
Fit to a single-basin job
22%3,500 W in the technical details scores more than 3,000 W, and more than 3.5 kW in the title alone. Naming sinks and excluding a shower scores more than a shower title with no spec table.
Amazon stars
22%The amazon.co.uk star average, divided by 5 and times 20, rounded to the nearest integer. A listing with no review line scores 0.
Review count
11%The number of ratings on that listing, from none up to 50 or more. None of these five has a large sample. No review line scores 0.
Price band in this set
12%Watts stated in the technical details score more than a title-only listing at a higher price. The top pick carries one award, so best value is the next listing.
These five rows are small electric instantaneous heaters, not cylinders and not showers. Prices are the amazon.co.uk shelf figures from 15 October 2026, from about £42.00 to about £60.99. Read the watts in the technical details before you compare a price. A 3.5 kW title with no spec table is not a 3.5 kW heater. A 3,000 W listing is the next class down. None of these five was laboratory tested, and none has a large review sample.
A 3.5 kW tankless water heater heats water only while the tap runs. There is no cylinder. The job in this set is one hand basin, or a very small sink, close to the outlet. People also buy one to replace a long draw-off from a distant cylinder, still for a basin only. A shopper who wants a shower is in the wrong category. You read the watts in the technical details, not only the title. 3,500 W at 230 V is 15.2 A. The Plugs and Sockets etc.
Two Generic listings say 3.5 kW and shower in the title. Neither technical-details block states wattage, voltage or flow, and neither has a review line. A shower title is not evidence the unit will run a UK cubicle.
Hyco’s rise formula gives about 25°C at 3.5 kW and 2 L/min. A 4 L/min claim and a 55°C claim cannot both hold from a cold inlet. The MRNIU prints both, and reviews report water around 18–30°C.
3,500 W at 230 V is about 15.2 A, above a BS 1363 13 A plug. A fitted three-pin plug does not change that. Calling a 3,000 W unit a 3.5 kW unit is the same sort of mistake. A new circuit is work for an electrician.
The first check is the wattage line in the technical details. The MRNIU states 3,500 W and 230 V. The Builrand and the Axelrivet state 3,000 W. The two Generic listings put 3.5 kW in the title and leave wattage, voltage and flow out of the spec table. A title is not a measurement. 3,500 W at 230 V is 15.2 A. That is above a 13 A plug. The Plugs and Sockets etc. (Safety) Regulations 1994 cover appliances designed for not more than 13 A.
The second check is what the maker says the heater is for, then the flow against the temperature. The MRNIU bullets name sinks and exclude showers, baths and whole-house use. The Builrand bullets aim at hand washing. The Generic titles say shower without a spec table. Ascot’s chart puts 3.5 kW on a basin, not a sink or a shower, at a 15°C inlet. Hyco’s formula is rise = kW × 14.3 ÷ litres per minute. At 3.5 kW and 2 L/min the rise is about 25°C.
Three typical situations, each with a recommendation from this comparison.
You want one hand basin, the flow kept low, and a supply designed for about 15 A. The MRNIU is the only listing here whose technical details state 3,500 W and 230 V, at about £42.00. It excludes showers. Reviews average 2.2 from 14, and some report lukewarm water.
You are comparing the next power down, not a stated 3,500 W element. The Axelrivet lists 3,000 W at about £44.99, with a bullet flow of 2.9 L/min and 3.1 from 5 reviews. One review reported about 4,200 W and heat only at a trickle.
The space under the basin is the constraint, and you have already read the heat and leak notes. The Builrand is the smallest body here, 11 cm by 19 cm and 1 kg, at 3,000 W and about £44.99. Eight reviews average 2.7, with little heat and one leak reported.
The MRNIU is the top pick in this set because it is the only listing whose technical details state 3,500 W and 230 V, at about £42.00, and the listing excludes a shower. The average is still 2.2 from 14 reviews, with water reported around 18–30°C, and reviewers describe a three-pin plug the spec table does not list. The Axelrivet is the best value beside that pick: 3,000 W at about £44.99, a stated flow, a one-year warranty, and 3.1 from 5 reviews. It is not a 3.5 kW heater. The two Generic rows claim 3.5 kW only in the title.
Axelrivet 3.0 kW under-sink
At about £44.99 it states 3,000 W, a flow and a one-year warranty, and it averages 3.1 from 5 reviews. It is the stronger of the two £44.99 units, and it is not a 3.5 kW heater.
Editorial
Peter F. is the editor for DIY & tools at productscompared.co.uk. Comparisons in this category are checked against amazon.co.uk listings, review evidence and public UK sources.
Guides on what to look for, how to use a product, and common mistakes.
Public UK sources used with the amazon.co.uk listings in this set; shelf prices from 15 October 2026.
This page contains affiliate links. A qualifying purchase can earn a commission at no extra cost to you. Prices and review counts are from amazon.co.uk listings captured on 15 October 2026. We did not laboratory-test these heaters.
