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Install an 80 litre electric water heater: what to check first

Updated: 21 October 2026

You are about to book someone, or you are tempted to fit a wall heater because you can work 15 mm pipe. An 80 litre unvented store is past the point where soldering skill is the qualification. You can measure the wall, read what the box omits, and plan the wait after switch-on. A competent person connects the store, the discharge, and the support. Peter F. used the five amazon.co.uk cards in our [80 litre hot water cylinder comparison](/hub/hot-water/80-litre-hot-water-cylinder) and public UK guidance, with listings read on 20 October 2026. There was no cable design and no heat-up test. A qualifying purchase can earn a commission at no extra cost to you.

You are about to book someone, or you are tempted to fit a wall heater because you can work 15 mm pipe. An 80 litre unvented store is past the point where soldering skill is the qualification.

Our top picks

TESY TESY 80 litre BiLight vertical

Best overall

TESY TESY 80 litre BiLight vertical
8.8/10about £234.99
View offer
Eldom Eldom Spectra 80 litre

Best value

Eldom Eldom Spectra 80 litre
8.6/10about £189.00
View offer
TESY TESY BiLight 80 litre horizontal

Rank 3

TESY TESY BiLight 80 litre horizontal
0.0/10about £229.99
View offer
On this page
  1. 1.Measure the wall and the route before you order
  2. 2.Read the included line as the kit list
  3. 3.Where you stop
  4. 4.The first heat is hours, not minutes

Measure the wall and the route before you order

The plain vertical TESY prints 44 × 50 cm at 24 kg empty, short for this volume. The Wi-Fi TESY prints 44 × 90 cm and a depth bullet of 455 m. The horizontal TESY prints 86 × 47 cm. The Eldom prints 82.5 cm wide by 45.7 cm high, so a vertical title will not fit a 50 cm-wide slot. Measure the niche and the path to the tundish before you pay. If a vertical card will not stand there, use the vertical or horizontal page.

Read the included line as the kit list

The horizontal TESY says cylinder only, and it names a 3 bar valve and a 1.5 mm cable as required and not included. That 1.5 mm line is the listing’s claim, not a cable design to copy onto the other heaters. The Wi-Fi TESY includes a wall bracket and not the bolts. On part number 306344, Modern Heat says the expansion vessel and a temperature-and-pressure valve are extra. The plain TESY says cylinder, and a UK review says no fittings and no cable arrived. The Thermex includes a 3-way safety valve and a wall anchor. The Eldom states a safety valve. A valve in one box does not mean the next ASIN has one.
TESY TESY 80 litre BiLight vertical

Testsieger

TESY TESY 80 litre BiLight vertical
8.8/10about £234.99
View offer

Where you stop

You stop before the connection. In England and Wales, an unvented store over 15 litres is notifiable under Approved Document G unless a competent-person installer self-certifies. The discharge uses a short metal pipe to a vertical tundish, with no more than 600 mm between the valve outlet and the tundish. A discharge joined straight into a waste is a contamination path. A new circuit, and work in a bathroom special location, is notifiable under Approved Document P. Three kilowatts at 230 volts is about 13 A, so a 3,000 W claim is commonly a wired circuit rather than a plug. Who should still open which listing is on the best in this set page.

The first heat is hours, not minutes

Once the store is filled, bled, and switched on, you wait. A rule of thumb, losses ignored, is about 2.1 hours to lift 80 litres through 45 degrees at 2 kW. The catalogue time of 2 hours 8 minutes belongs to a named 2,000 W TESY, not to the card that prints 1,500 kW. The horizontal card prints 3,000 W, and a retailer table for a horizontal BiLight 80 prints 2,000 W. A bullet that says 24 minutes of hot water is the seller’s claim, not a cold-start measurement. If the element row is contradictory, the wait is unknown until the plate is read.

Common questions

Can I fit this myself if I can solder 15 mm pipe?
Pipe skill is not the qualification. An unvented store over 15 litres in England and Wales needs a competent person, or a building notice, and an installation record. The horizontal TESY does name 15 mm compression, one cold in and one hot out, which tells you the pipe size on that card. It does not authorise you to connect the store, the discharge, or a new circuit. Book the scheme installer for that work.
What should be on site before the installer arrives?
The niche measured, the wall identified, and a note of what the listing says is missing. For the horizontal TESY that note is a valve and a cable the card says are not in the box. For the Wi-Fi TESY it is bolts, plus an expansion vessel and a temperature-and-pressure valve on the matching retailer page. For the Thermex the valve and the wall anchor are stated as included, and the manual may not be in English. Have the data plate checked against the advert before anyone starts.
Is a 13 A plug enough for 3 kW?
Three kilowatts at 230 volts is about 13 A, which is the top of a BS 1363 13 A fuse, so a continuous 3 kW storage heater is commonly a wired circuit rather than a plug. None of these cards names a BS 1363 plug as a designed UK lead. A plug does not remove Part P, and a new circuit is notifiable. Do not copy a cable size from the horizontal listing’s 1.5 mm remark onto a different heater.
What do I do if the tundish drips?
Stop using it as a minor drip you can live with. Discharge at the tundish is the visible warning the guidance describes. Call the competent person who certified the store, or a competent unvented installer if you do not have that record. Do not cap the pipe, and do not keep raising the thermostat to get more heat while water is leaving the safety device.
Does the Thermex network-operator line mean no building notice?
No. That bullet says installation needs no permission from the network operator and that the unit is not a high-voltage heater. It does not name a UK competent-person scheme, Part G, or Part P. An 80 litre unvented store is still over the 15 litre line. A new circuit is still notifiable. Treat the bullet as a claim about a network operator, not as permission to fit the heater yourself.

Related pages

80 litre buying guide

80 litre hot water cylinder

Best 80 litre hot water cylinder: a short shortlist

Is 80 litres enough for a shower in one UK bathroom

Vertical or horizontal hot water cylinder: which fits

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these five listings were taken from the listing files read on 20 October 2026. Page updated 21 October 2026.

  1. Approved Document G (2024 amendments) (retrieved 20 October 2026)
  2. Approved Document P (2013) (retrieved 20 October 2026)
  3. HSE hot and cold water (retrieved 20 October 2026)
  4. HSE cylinder checks (retrieved 20 October 2026)
  5. Retained Regulation 812/2013 (retrieved 20 October 2026)
  6. GOV.UK energy labelling of products (retrieved 20 October 2026)
  7. Hot Water Association sizing (retrieved 20 October 2026)
  8. TESY BiLight 80 datasheet (retrieved 20 October 2026)