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Best 27kW instantaneous water heater

Updated: 21 October 2026

You are comparing the heaters kept on amazon.co.uk and you want one name, with a reason to leave the others. The best 27kW instantaneous water heater in this set is the listing specified at 400 V, because that is the supply this output uses in the UK. Best here means that match, not a trophy and not a lab result. Prices and stars are the figures held for this comparison, checked on 19 October 2026. The full grid is on the [27kW instantaneous water heater comparison](/hub/hot-water/27kw-instantaneous-water-heater). Peter F. did not run these units. A qualifying purchase can earn a commission at no extra cost to you.

You are comparing the heaters kept on amazon.co.uk and you want one name, with a reason to leave the others.

Our top picks

WINTEMP WINTEMP YQ-WN27K

Best overall

WINTEMP WINTEMP YQ-WN27K
1.8/10about £408.53
View offer
GRS GRS 27 kW

Rank 2

GRS GRS 27 kW
1.6/10about £388.71
View offer
Stiebel Eltron Stiebel Eltron DHE 27 Set

Rank 3

Stiebel Eltron Stiebel Eltron DHE 27 Set
6.9/10about £821.57
View offer
On this page
  1. 1.What best can mean here
  2. 2.The 400 V listing
  3. 3.The two 240 V listings
  4. 4.If you wanted 3i or a selectable output

What best can mean here

This page splits three listings by the voltage on the amazon.co.uk page. A 27 kW instantaneous heater in Britain is a 400 V three-phase appliance, about 39 A per phase. A 240 V title with the same kilowatt number is a different electrical product, even at half the price. There is no UK lab ranking here, and a thin star line is not a quality verdict. The top pick is the row whose supply field says 400 V. If you do not have 400 V, none of the three is the heater for a normal single-phase flat.

The 400 V listing

The top pick is the Stiebel Eltron DHE 27 Set, B08L5B34YH, at £821.57. Amazon.co.uk shows 2.9 from 2 ratings and no review text, so skip it if you need a written UK ownership record. Choose it when a competent person has confirmed 400 V. The title says 27 kW and the wattage field says 24,000 W. Stiebel rates 27 kW on 400 V and 24.4 kW on 380 V, with 4i control, ECO and IP25. Listing model 202657 does not match UK product number 204285. Match the carton. Heater Shop prints both numbers at £837.79 including VAT, which is context, not this amazon capture. The comparison sheet gives 13.8 litres per minute at a 28 °C rise, one winter shower.
WINTEMP WINTEMP YQ-WN27K

Testsieger

WINTEMP WINTEMP YQ-WN27K
1.8/10about £408.53
View offer

The two 240 V listings

Skip the WINTEMP YQ-WN27K, B0FPX5C9Y1, at £408.53, for a UK home. The page says 240 V, 27 kW, 6.5 gallons per minute and 140 °F, with 5.0 from 1 rating and no text. ETL in the bullets is not a UK water-fittings approval. Skip the GRS model JN, B0C35HR76V, at £388.71, for the same supply reason. The title says whole-house water tank and the bullets say tankless, with a 2 litre capacity. Amazon shows 4.0 from 69, and the review text is marked United States. The contrast is on the 240 V tankless page.

If you wanted 3i or a selectable output

The DHE in this set is the 4i control, meant to hold the set temperature until output runs out. The DHB-E 27 LCD is the 3i alternative on the same 27 kW, 39 A, 400 V frame, and it holds temperature only up to the output limit. It is not a kept row, so this page does not score it. Heathfield LED has listed a DHB-E 27 at £532.80 including VAT, as context only. CLAGE sells 400 V heaters commissioned at 18, 21, 24 or 27 kW. A CLAGE DSX Touch, B08P28F3C5, was not kept, so it is not a pick here.

Common questions

Which listing is actually 400 V?
Only the Stiebel Eltron DHE 27 Set, B08L5B34YH, at £821.57. The supply field says 400 V. WINTEMP B0FPX5C9Y1 at £408.53 and GRS B0C35HR76V at £388.71 are both specified at 240 V. Same kilowatt number, different supply. If you do not have 400 V three-phase, the 400 V listing is not yours to fit either.
Why does the Stiebel row say both 24 kW and 27 kW?
The amazon title and style field say 27 kW. The wattage field says 24,000 W and the heat-output field says 24 kW. Stiebel's UK data rates 24.4 kW at 380 V and 27 kW at 400 V. Treat that as a listing clash plus a real voltage effect, and match the nameplate. The listing model is 202657 and the current UK product page uses 204285.
Is the £388 unit a better buy because of 69 reviews?
No. The GRS page is 240 V, the title and the bullets disagree about tank and tankless, and the review text is marked United States. A larger star count on the wrong supply is not a better UK heater. The 400 V Stiebel listing has only 2.9 from 2 and no text, which is also too thin to call a durability record. Neither star line replaces the voltage check.
What is 4i compared with 3i?
On Stiebel's brochure, 4i is the DHE control: it is meant to hold the set temperature until output runs out, with ECO and memory buttons. 3i is the DHB-E control, which holds temperature only up to the output limit. Both sit on the same 27 kW, 400 V, 39 A frame. Only the 4i DHE 27 Set is in this amazon set. The DHB-E is named so you do not think it was scored here.
Who should skip WINTEMP and GRS?
Skip both if the job is a UK instantaneous heater at this output. They are specified at 240 V, they use US units or US review text, and neither listing documents them as a 400 V appliance. The price gap, about £389 to £409 against £821.57, is the reason they look attractive. It does not change the supply.
Is there a UK review base for the Stiebel listing?
Not in this capture. Amazon.co.uk shows 2.9 from 2 ratings and no review text. That is too small to treat as owner experience, good or bad. Heater Shop's page is a retailer, not a substitute review file. Decide on the 400 V specification and the nameplate, and treat the stars as a gap.
Does best mean the most powerful shower for a family at once?
No. About 13 to 13.8 litres per minute at a 28 to 30 °C rise is the winter flow published for 27 kW. Stiebel says a sink during a shower may affect a DHE at this output. Best on this page means the correct supply among three listings, not two showers running together.

Related pages

27kW instantaneous water heater buying guide

27kW instantaneous water heater on three-phase

27kW instantaneous water heater

How to use an instantaneous water heater at 27 kW output

240V tankless water heater UK, not the 400 V heater

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these three listings were read on 19 October 2026. Page updated 21 October 2026.

  1. Approved Document G, with 2024 amendments (retrieved 19 October 2026)
  2. Approved Document P, 2013 (retrieved 19 October 2026)
  3. Water Supply (Water Fittings) Regulations 1999 (retrieved 19 October 2026)
  4. HSE, landlords and legionella (retrieved 19 October 2026)
  5. Stiebel Eltron UK, DHE 27 Set (retrieved 19 October 2026)
  6. Stiebel Eltron UK comparison sheet (retrieved 19 October 2026)
  7. Stiebel Eltron UK, three-phase water heating (retrieved 19 October 2026)
  8. Flexiheat UK, electric instantaneous water heaters (retrieved 19 October 2026)
  9. amazon.co.uk, Stiebel Eltron DHE 27 Set B08L5B34YH (retrieved 19 October 2026)