The best Bosch tankless water heaters, compared.
Top pick: Bosch Tronic 4000 10.5 kW – Highest listing score in the set: 10.5 kW agreed across title, wattage and heat output, one review naming a kitchen sink and a power shower, at about £239.38. Best value: Bosch Tronic 4000 8.5 kW – Lowest shelf price at about £236.63, and the only point-of-use row with a stated flow of 1.5 gal/min. Updated 17.10.2026.
A Bosch tankless water heater is one of five Bosch electric models on amazon.co.uk: three 4000 C point-of-use units at 6.5, 8.5 and 10.5 kW, and two 6100 C units at 18 and 27 kW. Part numbers 7738007416, 7738007417, 7738007418, 7738007420 and 7738007421 match Bosch US engineering sheets for 208/240 V at 60 Hz and threads, not a UK 13 A plug. UK mains are nominally 230 V at 50 Hz, so a 60 Hz sheet is a stop-and-check, not a hidden approval. That is not a review winner: the star line is 3.1 from two ratings, and three files have no line. Match the fixture and the supply first, using the [Bosch tankless water heater buying guide](/hub/hot-water/bosch-tankless-water-heater/sub/bosch-tankless-water-heater-buying-guide). A European 4000 ET, for example article 7736504689, is a different product: 230 V and a much smaller body.
A Bosch tankless water heater is one of five Bosch electric models on amazon.co.uk: three 4000 C point-of-use units at 6.5, 8.5 and 10.5 kW, and two 6100 C units at 18 and 27 kW.
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Personal buying guide
Question 1 of 2
What job are you matching?
The Bosch Tronic 4000 10.5 kW is the highest point-of-use wattage kept in this comparison, listed at £239.38, which is £2.75 above the cheapest row. One written review, inside a 3.1 average from two ratings, says it must be fitted properly and that it is working a kitchen sink and a power shower. The title, the wattage and the heat output all say 10.5 kW, and the bullets name one or more sinks with activation from 0.55 gal/min. You get no listed flow on this page, and the power source says corded electric without naming a plug. Efficiency is 98% on the specification line and 96% in the bullets. A 55-gallon capacity cell was set aside because the bullets say the heater holds no water, and the title prints 13 x 8.5 x 4.5 with no units. It is the top pick on the score for this set, which is not the same as a settled review verdict from two ratings.
Pros
Cons
Best for: A point-of-use sink where you want the highest Tronic 4000 wattage in this set.
Less suitable: Anyone who needs a listed flow, a named plug, or a review sample larger than two.
Specifications
Common questions
What does the review say it is used for?
The only review text says it must be fitted properly and that it is working a kitchen sink and a power shower.
Why is capacity not shown?
The capacity cell says 55 gallons. The bullets say the heater does not hold water, so capacity is left off the table.
What power is listed?
10,500 watts, and the heat-output line says 10.5 kW.
The Bosch Tronic 4000 6.5 kW is the lowest-wattage point-of-use heater in this set. The listing prices it at £245.74, says it is hard-wired, and puts it under a sink with activation from 0.55 gal/min. Two amazon.co.uk reviews average 3.1: one says the install was easy and that it saved space in a small studio, and the other calls it a waste of money after a recent install without naming a fault. The title and the wattage line both say 6.5 kW, but a heat-output cell says 65 kW, so that cell is not used. You will not find a listed flow or a warranty line, and the bathroom question on the page is unanswered. The case is 21.6 cm wide, 33 cm high and 11.4 cm deep, at 2.39 kg. Inside this set it is the dearest of the three Tronic 4000 rows for the least power.
Pros
Cons
Best for: A small studio under-sink job where you are matching a hard-wired 6.5 kW listing.
Less suitable: A bathroom the page does not confirm, or a price-per-kilowatt comparison inside this set.
Specifications
Common questions
What power does the listing state?
The title and the wattage line say 6.5 kW. A separate heat-output cell says 65 kW, so that cell is not shown.
How is the supply described?
The listing says hard-wired. It does not name a plug.
What do the two reviews say?
One says it was easy to install and saved space in a small studio. The other calls it a waste of money after a recent install and names no fault.
The Bosch Tronic 4000 8.5 kW is listed at £236.63, the lowest price of the five, and it is the only point-of-use row with a stated flow of 1.5 gal/min. Activation is given as 0.55 gal/min, and the bullets describe an under-sink wall unit in white plastic, model 7738007417, weighing 2.41 kg. Wattage and heat output both read 8.5 kW. This saved listing has no Customer Reviews line, so you have no star rating to go on. The power source says corded electric and names no plug, and shower use is not confirmed. Efficiency is 98% on the specification line and 96% in the bullets, and a capacity cell says 0.55 gal next to a bullet that says the heater holds no water. On shelf price and a printed flow figure, it is the best value in the set.
Pros
Cons
Best for: An under-sink point-of-use job where you want the lowest price and a listed flow of 1.5 gal/min.
Less suitable: A shower the listing does not confirm, or a purchase you want to check against reviews.
Specifications
Common questions
Does the listing say it suits low-flow taps?
Yes. The bullets say activation can be as low as 0.55 gal/min and that it is aimed at low-flow taps.
What material is listed?
Plastic. The housing bullet also says white plastic.
Is there a star rating?
No. This file has no Customer Reviews line.
The Bosch Tronic 6100 27 kW is listed as hard-wired at 27,000 W, and at £662.81 it is cheaper than the 18 kW row. The bullets state a 5-year limited warranty, which the Tronic 4000 listings in this set do not print. Those same bullets call it an under-sink unit for low-flow taps, which clashes with 27 kW, and the shower question is unanswered. There is no Customer Reviews line. Flow and depth are not usable, efficiency is 95% on the specification line and 96% in the bullets, and a 55-gallon capacity cell conflicts with wording that the heater holds no water. The case is listed at 21.6 cm wide, 33 cm high and 7.85 kg. It costs less than the 18 kW listing, and it is not the best value, because the electrical job is larger and the page does not agree with itself. If you came for a small low-flow heater, this title is the wrong row.
Pros
Cons
Best for: A hard-wired 27 kW indoor job where the 5-year limited warranty line is why you are on this page.
Less suitable: An under-sink low-flow tap, or anyone treating the lower price than 18 kW as the best value.
Specifications
Common questions
Is it described as hard-wired?
Yes. The power-source line says hard-wired.
What warranty do the bullets state?
A 5-year limited warranty. No longer warranty text is in the file.
Does the listing say it can feed a shower?
The bullets do not answer that question, so shower use is not confirmed.
The Bosch Tronic 6100 18 kW is the dearest row in this set at £706.84. Wattage and heat output both say 18 kW, and the style line says indoor installation. The bullets still describe an under-sink point-of-use unit, and the power source says corded electric with no plug. This file has no Customer Reviews line. The flow cell repeats the 0.55 gal/min activation figure instead of a separate delivery rate, the depth is given as 4.5 in beside centimetre width and height, and the material line says plastic copper. A 55-gallon capacity cell was discarded. The listed case is 50.8 cm wide and 33 cm high, at 9.06 kg, so you are looking at a much larger unit than the Tronic 4000 rows, with listing text that still reads like a small under-sink heater.
Pros
Cons
Best for: Only if you are matching model 7738007420 and can set the under-sink wording aside.
Less suitable: An under-sink tap, or a buyer who needs reviews and a flow figure that is not the activation rate.
Specifications
Common questions
What placement does the listing claim?
The bullets say it fits under sinks for point-of-use use. The style line says indoor installation.
Why is capacity left off?
The capacity cell says 55 gallons and the bullets say the heater does not hold water.
Is there a star rating?
No. This file has no Customer Reviews line.
Scores use only the five amazon.co.uk Bosch listings kept in this comparison on 15 October 2026. They are not a laboratory test and they do not rank the wider UK water-heater market. The figure on each card is that listing score divided by 10. Two listings show 3.1 from two reviews. Three have no Customer Reviews line. The score judges the listing inside this set. It does not crown a review winner.
Amazon rating and written review
25%A real star line and a review that names a job score here. Most of the points stay withheld when the sample is two, and a missing Customer Reviews line scores nothing.
Listing matches the job
25%Title, wattage and the stated use should describe the same heater. An under-sink bullet on an 18 or 27 kW title is marked down, as is a supply line that names no plug.
Buyer-facing numbers
20%Flow, activation, dimensions and weight count when they survive a conflict check. A cell that fights the bullets, such as 65 kW or 55 gallons, is not used.
Price against the listing
20%Shelf price is judged against what the page actually is inside this set. The lowest price helps only when the row is still a point-of-use heater with a usable figure.
Internal consistency
10%Wattage, heat output, efficiency and capacity should agree. Split percentages and a capacity cell beside a no-stored-water bullet reduce the score.
Match the article number, the job and the supply before you compare shelf prices. A star line of 3.1 from two reviews cannot do that work.
A Bosch tankless water heater on these amazon.co.uk pages heats water as it passes through. It does not store a tank. The five listings kept in this category are the US C series: Tronic 4000 C at 6.5, 8.5 and 10.5 kW, and Tronic 6100 C at 18 and 27 kW. The article numbers are 7738007416, 7738007417, 7738007418, 7738007420 and 7738007421. A European Tronic 4000 ET, for example article 7736504689, is a different product: 230 V and a much smaller body.
Corded electric on these pages names no plug. Over about 3 kW is not a 13 A ring-main job. The 6.5 kW and 27 kW rows are the ones that say hard-wired.
A heat-output cell of 65 kW, a 55-gallon capacity, and a flow figure that only repeats the activation rate are conflicts. The bullets say these heaters hold no water.
The 27 kW title is a Tronic 6100 whole-house heater. The same bullets that mention a 5-year limited warranty still talk about an under-sink low-flow tap. That wording does not make it a basin heater.
Confirm the article number before the price. These ASINs are the US C series: 7738007416, 7738007417 and 7738007418 for the Tronic 4000, and 7738007420 and 7738007421 for the Tronic 6100. A European Tronic 4000 ET, such as 7736504689, is a different and smaller 230 V product. Do not copy its flow or its body size onto these rows. The 4000 C is a non-thermostatic sink heater. Power is selected in steps, and the outlet temperature falls if you open the tap further.
Check the supply before the shelf price. Over about 3 kW is not a 13 A ring-main job, and corded electric on these pages names no plug. Arithmetic at 230 V is about 28 A, 37 A and 46 A for 6.5, 8.5 and 10.5 kW on one circuit. The 18 kW US sheet wants three 30 A double-pole breakers, about 75 A at 240 V. The 27 kW sheet wants three 40 A double-pole breakers, about 112.5 A at 240 V. The 6.5 kW and 27 kW listings say hard-wired. Flow is the other half of the same check.
Three typical situations, each with a recommendation from this comparison.
You want the strongest Tronic 4000 in this folder for a basin, and you can live with two ratings. The 10.5 kW listing is about £239.38. Title, wattage and heat output agree, and one review names a kitchen sink and a power shower after proper fitting. There is no listed flow.
You want the cheapest row that still prints a flow. The 8.5 kW listing is about £236.63, with 1.5 gal/min stated and activation at 0.55 gal/min. There is no Customer Reviews line, and shower use is not confirmed on the page.
You are looking at a whole-house load and the 5-year limited warranty line is why this page is open. The 27 kW listing is hard-wired at about £662.81, cheaper than the 18 kW row. Stop unless an electrician can feed three high-current circuits. The under-sink bullets do not match 27 kW.
The highest listing score is the Bosch Tronic 4000 10.5 kW, so that row is the top pick: about £239.38, with title, wattage and heat output agreed at 10.5 kW, and one review that names a kitchen sink and a power shower. The sample is two ratings at 3.1, and there is no listed flow. The best value is the Bosch Tronic 4000 8.5 kW at about £236.63, the lowest shelf price and the only point-of-use row with a stated flow. It is only £2.75 less than the 10.5 kW row. The 27 kW listing is cheaper than the 18 kW listing and is not the value pick, because the supply job is larger and the page does not agree with itself. None of this is a lab test.
Bosch Tronic 4000 10.5 kW
Highest listing score in the set: 10.5 kW agreed across title, wattage and heat output, one review naming a kitchen sink and a power shower, at about £239.38.
Bosch Tronic 4000 8.5 kW
Lowest shelf price at about £236.63, and the only point-of-use row with a stated flow of 1.5 gal/min.
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.
Sources from the research digest. amazon.co.uk prices in this comparison were captured on 15 October 2026.
This page contains affiliate links to amazon.co.uk. If you buy through them, we may earn a commission at no extra cost to you. Prices, stars and review counts are the UK listing figures in this comparison. We did not lab-test these heaters.
