Best Bosch tankless water heater
Updated: 17.10.2026
You want one Bosch listing per job, and the star row will not give it to you. Two of the five amazon.co.uk listings show 3.1 out of 5 from two reviews, and three have no Customer Reviews line. On 15 October 2026 the point-of-use prices ran £236.63, then £239.38, then £245.74. The best Bosch tankless water heater, on this page, means the smallest listing whose job matches a supply you have already checked. The [main comparison](/hub/hot-water/bosch-tankless-water-heater) holds the full rows. The Products Compared editorial team did not laboratory-test these heaters. A qualifying purchase can earn a commission at no extra cost to you.
You want one Bosch listing per job, and the star row will not give it to you. Two of the five amazon.co.uk listings show 3.1 out of 5 from two reviews, and three have no Customer Reviews line.
You want one Bosch listing per job, and the star row will not give it to you. Two of the five amazon.co.uk listings show 3.1 out of 5 from two reviews, and three have no Customer Reviews line. On 15 October 2026 the point-of-use prices ran £236.63, then £239.38, then £245.74. The best Bosch tankless water heater, on this page, means the smallest listing whose job matches a supply you have already checked. The main comparison holds the full rows. The Products Compared editorial team did not laboratory-test these heaters. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Listed flow | Reviews | Supply | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Bosch Bosch Tronic 4000 10.5 kW | n/a | 3.1 (2 ratings) | Corded electric | 5.4 | about £239.38 | View offer |
| Alternative |  Bosch Bosch Tronic 4000 6.5 kW | n/a | 3.1 (2 reviews) | Hard-wired | 4.4 | about £245.74 | View offer |
| Preis-Tipp |  Bosch Bosch Tronic 4000 8.5 kW | 1.5 gal/min | No review line | Corded electric | 5.1 | about £236.63 | View offer |
On this page
Why there is no star winner
The 6.5 kW Tronic 4000 (B0BWKBQ1TY, part 7738007416) is the only listing with two written comments. 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 fitting and names no mechanical fault. The 10.5 kW Tronic 4000 (B0BWKDBT8F, part 7738007418) shows the same 3.1 from two ratings, with one review text: it must be fitted properly, and that household is using it on a kitchen sink and a power shower.
The 8.5 kW, 18 kW and 27 kW files have no Customer Reviews line. Two short reviews cannot sort five heaters. If you came for a review champion, amazon.co.uk has not produced one. The useful split is the job, starting with the buying guide.
Point-of-use shortlist
A single basin is the narrowest job. Look at the 6.5 kW listing at £245.74 when a jug test shows the tap can pass about 0.55 gal/min, about 2.1 litres per minute, and an electrician has accepted a dedicated hard-wired circuit. This row does say hard-wired, which is clearer than Corded Electric on the other two. Skip it when you wanted the lowest price or a printed delivery flow. The flow cell is n/a, and £245.74 is the dearest of the three.
For more heat at the same sort of sink, choose between the 8.5 kW listing at £236.63 (B0BWK7W2YK, part 7738007417) and the 10.5 kW listing at £239.38. The 8.5 kW row is the only one with a stated flow, 1.5 gal/min, and the lowest price in the set. It has no reviews, and Corded Electric names no plug. The 10.5 kW row costs £2.75 more, and the title and heat output agree at 10.5 kW. Its listed flow is n/a. Skip the 10.5 kW row if you are reading that power-shower sentence as a specification.
The 18 kW and 27 kW listings
The 18 kW Tronic 6100 (B0BWKCCQ1V, part 7738007420) is £706.84, with no review line. The style line says indoor installation. The bullets still say it fits under sinks, and the flow cell prints 0.55 gal/min, the same figure the smaller listings use as activation. On Bosch’s US sheet this part number is a thermostatic heater on three 30 A double-pole breakers.
The 27 kW Tronic 6100 (B0BWKCVFTW, part 7738007421) is £662.81, so £44.03 cheaper, and the bullets state a 5-year limited warranty. The power source says hard-wired. The same bullets then claim an under-sink fit and 0.55 gal/min, which is the small-unit wording on a 27,000 W title. Flow and depth are n/a. The US sheet asks for three 40 A double-pole breakers. The breaker count goes up as the shelf price goes down. Buy either only after the supply can feed those circuits. If the supply is unknown, do not buy. A normal single-phase flat with no design for that load should skip both.
What to skip even if the price looks right
Skip the 65 kW cell on the 6.5 kW listing, every 55-gallon capacity cell, and 0.14 cubic metres per minute on the 27 kW flow line. Skip corded as proof of a UK 13 A plug. No listing names one. Skip the 27 kW listing because it is cheaper than the 18 kW listing: the electrical work is larger.
Skip the 10.5 kW review as a reason to replace a shower. One household mentioned a power shower. The bullets describe sinks. What we will not crown is a best overall unit. The conditional picks above are reversible the moment the electrician says the supply is wrong.
Common questions
Which listing has the best reviews?
The 6.5 kW and 10.5 kW listings both show 3.1 from two reviews. The 6.5 kW comments disagree: an easy studio install against a waste of money. The 10.5 kW file has one note about fitting, a sink and a power shower. The other three listings have no review line. That record is too thin to rank the set.
Is the cheapest 8.5 kW unit the one to buy?
Look at it when you want the lowest price here, £236.63, plus a stated flow of 1.5 gal/min, and the supply can take 8.5 kW. There are no reviews, and Corded Electric names no plug. The 10.5 kW listing is £2.75 more and has one written review. Decide on the measured flow and the circuit, not on the £2.75.
When is 6.5 kW enough?
Use it for one basin when the tap passes about 0.55 gal/min and the circuit is dedicated and hard-wired. Bosch’s 4000 C sheet, at a rise of about 43°C, puts that model near 2.2 litres per minute. Look at 8.5 kW or 10.5 kW when you need more flow and the supply can take it. At £245.74, the 6.5 kW listing is the dearest of the three.
Should I buy 27 kW because it costs less than 18 kW?
The £662.81 price against £706.84 is real, and so is the 5-year warranty bullet. The US sheet steps from three 30 A double-pole breakers at 18 kW to three 40 A at 27 kW. The amazon bullets still describe an under-sink tap. A lower price with a larger supply and no reviews is not the better buy.
Can the 10.5 kW review mean it is good for a shower?
The only text says the unit must be fitted properly and mentions a kitchen sink and a power shower. The bullets still describe sinks and 0.55 gal/min activation. A UK electric shower is its own outlet, usually 7.5–10.8 kW, on 15 mm connections. One sentence is not a reason to swap the products.
What should a normal single-phase flat skip?
Skip the 18 kW and 27 kW listings until a supply for three high-current circuits has been designed. Skip every listing if the only point is a 13 A socket. At 230 V, 6.5 kW is already about 28 A. Stay with the question until that conversation has happened.
Related pages
Sources
Sources from the research digest. amazon.co.uk prices in this comparison were captured on 15 October 2026.
- Bosch Tronic 4000 C engineering submittal (Feb 2023) (retrieved 15 October 2026)
- Bosch Tronic 4000 C installation manual (Nov 2025) (retrieved 15 October 2026)
- Bosch Tronic 6100 C engineering submittal (Feb 2023) (retrieved 15 October 2026)
- Approved Document G (England, 2024 amendments) (retrieved 15 October 2026)
- Building Regulations &c. (Amendment) Regulations 2012, regulation 6 (retrieved 15 October 2026)
- Consumer Rights Act 2015, goods terms (retrieved 15 October 2026)
- Stiebel Eltron UK sizing FAQ (retrieved 15 October 2026)
- IET Part P FAQ (England and Wales) (retrieved 15 October 2026)