By Emily Rivers
Last updated 7th September 2022

An unvented hot water cylinder receives cold water directly from the mains water supply and supplies all of the hot taps, hot water at mains pressure.

The cold water comes into the unvented hot water cylinder, is then heated by either an immersion heater or gas from a boiler before being sent to the hot water tap requesting hot water.

Unvented hot water cylinders can be both direct or indirect;

  • direct unvented cylinder uses the electricity to heat water using immersion heaters
  • indirect unvented cylinder uses gas from a boiler to heat the water 

In theory, as the water is fed off the mains supply, the pressure sent to showers and other taps should be a better stronger pressure than a gravity fed system of a vented hot water cylinder. Of course, this is as long as the mains on your road is a decent strong water pressure.

Why install an unvented cylinder?

If space is a premium (like in so many UK homes) then an unvented system is the way to go. An unvented ‘sealed’ system does away with the need for a gravity fed water tank in the loft. Unvented cylinders come in slimline options taking up even less space, a well-known brand to look out for is Gledhill's Stainless Lite Plus range which can be installed almost anywhere. Having water come off the mains should always give a better flow rate to the hot water taps in the property.

Another great unvented cylinder option is Megaflo manufactured by Heatrae Sadia (often misspelt as Megaflow system or Megaflow boiler) is a popular choice for a stainless steel unvented cylinder that stores hot water as part of a central heating system.

Reasons that make the Megaflo popular is;

  • water pressure in the system is consistent even if more than one outlet is being used at the same time, so it is suitable for families
  • Megaflo cylinders are easy to install, and parts are easier to replace and maintain
  • A Megaflo system is compatible with solar PV
  • The system is fitted with several different safety features, including a thermostat to shut the boiler down when it has reached the correct temperature. If it becomes too hot, the Temperature/Pressure Relief Valve (TPRV) would dump water out of the cylinder into a drain to reduce pressure
Cost to install an unvented hot water cylinder

Can I replace my vented cylinder with an unvented cylinder?

In short, yes. A vented system has been plumbed in with the knowledge that water will only be fed by gravity, therefore upgrading a system and replacing a vented with an unvented system sometimes requires the heating engineer to replace pipework to ensure that the pipes and joints can handle water flowing through at a higher pressure. This is especially necessary if it is older pipework.

A lot of UK homes prefer to upgrade the system to the unvented hot water cylinder to make use of the space that has been housing a water feed tank. Another idea is if you have a combi boiler, you can also install an unvented hot water cylinder to the system. This will help with the demand of a home with multiple bathrooms and where the demand for hot water can be simultaneously from different hot taps.

How much will it cost to replace an unvented hot water cylinder?

Replacing an unvented hot water cylinder is a pricey job. The cylinder alone can cost from £600 and then on top of this cost is the price of labour, which might include your heating engineer and a helper needing a full day to install and fit the unvented cylinder. 

If the heating engineer is upgrading the system and removing a vented cylinder to fit an unvented hot water cylinder, this will need the extra time of ensuring pipework can handle the possibly higher pressure and means labour costs will run into an extra day of work.

Cost to replace an unvented hot water system

Per

Average total labour cost

Replacing an unvented hot water cylinder

Per day

£450

Installing a Megaflo system

Per day

£450

Upgrading a vented to an unvented hot water cylinder

Per day

£650

Maintaining an unvented hot water cylinder

Per hour

£90

Diagnosing a fault on an unvented hot water cylinder

Per hour

£90

Is it time to replace my unvented hot water cylinder?

An unvented hot water cylinder has a longer lifespan than a vented cylinder, and as long as they are maintained, they should last for 30 plus years.

 If you notice damp patches around the cylinder or any signs of leaks, the cylinder may have a pin-hole or a crack and may be time to replace the cylinder before damage is caused to your home.

Another sign of a cylinder needing replacing is if it is filled with limescale and no longer heating water effectively or becomes noisy during the heating of the water.

When it comes time to replace your cylinder, if replacing with a new unvented hot water cylinder, the choices available aside from direct or indirect, include;

  • standard unvented cylinder
  • pre-plumbed unvented cylinder
  • horizontal unvented cylinder
  • slimline unvented cylinder
  • solar unvented cylinder

Which cylinder should be installed, vented or unvented?

Both vented and unvented cylinders come with their own set of advantages and disadvantages. Older UK properties tend to already be fitted with a vented system, and therefore at the time of replacement it is cheaper to just install a modern version of the same type of system.

Newer properties are fitted with either combi systems or unvented "sealed" systems. Unvented is a better choice between vented and unvented for the space saving as well as for the consistent higher pressure, but if the mains water pressure coming into your home is not a decent pressure, then a vented cylinder system would be the better choice for your home. Eliminating the need for the water tank in the loft also avoids the damage of another potential area for a water leak and pipes freezing in winter. There is also no concern of the threat of contaminated water in case any debris gets into the water tank in the loft.

The downside to an unvented system is the higher cost of installing the hot water cylinder and the on-going maintenance needs.


Estimates for common heating engineer jobs;

Rates for other trades

Fit or replace an unvented hot water cylinder cost in the UK
Fit or replace an unvented hot water cylinder cost in the UK (excluding VAT or callout charges)
Location in UKFit or replace an unvented hot water cylinder cost
Fit or replace an unvented hot water cylinder near Aberdeen£573
Fit or replace an unvented hot water cylinder near Amber Valley£487
Fit or replace an unvented hot water cylinder near Angus£545
Fit or replace an unvented hot water cylinder near Arun£555
Fit or replace an unvented hot water cylinder near Ashfield£481
Fit or replace an unvented hot water cylinder near Aylesbury Vale£571
Fit or replace an unvented hot water cylinder near Barnsley£477
Fit or replace an unvented hot water cylinder near Basildon£529
Fit or replace an unvented hot water cylinder near Basingstoke & Deane£565
Fit or replace an unvented hot water cylinder near Bassetlaw£495
Fit or replace an unvented hot water cylinder near Bath & North East Somerset£535
Fit or replace an unvented hot water cylinder near Bedford£577
Fit or replace an unvented hot water cylinder near Belfast£453
Fit or replace an unvented hot water cylinder near Birmingham£481
Fit or replace an unvented hot water cylinder near Blackburn£469
Fit or replace an unvented hot water cylinder near Blackpool£499
Fit or replace an unvented hot water cylinder near Bolton£499
Fit or replace an unvented hot water cylinder near Bournemouth£557
Fit or replace an unvented hot water cylinder near Bracknell Forest£593
Fit or replace an unvented hot water cylinder near Bradford£473
Fit or replace an unvented hot water cylinder near Braintree£525
Fit or replace an unvented hot water cylinder near Breckland£489
Fit or replace an unvented hot water cylinder near Bridgend£463
Fit or replace an unvented hot water cylinder near Brighton£541
Fit or replace an unvented hot water cylinder near Bristol£523
Fit or replace an unvented hot water cylinder near Broadland£537
Fit or replace an unvented hot water cylinder near Broxtowe£479
Fit or replace an unvented hot water cylinder near Bury£493
Fit or replace an unvented hot water cylinder near Caerphilly£463
Fit or replace an unvented hot water cylinder near Calderdale£461
Fit or replace an unvented hot water cylinder near Cambridge£567
Fit or replace an unvented hot water cylinder near Canterbury£509
Fit or replace an unvented hot water cylinder near Cardiff£471
Fit or replace an unvented hot water cylinder near Carmarthenshire£405
Fit or replace an unvented hot water cylinder near Charnwood£463
Fit or replace an unvented hot water cylinder near Chelmsford£519
Fit or replace an unvented hot water cylinder near Cheltenham£617
Fit or replace an unvented hot water cylinder near Cherwell£573
Fit or replace an unvented hot water cylinder near Chester£459
Fit or replace an unvented hot water cylinder near Colchester£521
Fit or replace an unvented hot water cylinder near Conway£423
Fit or replace an unvented hot water cylinder near Coventry£479
Fit or replace an unvented hot water cylinder near Crewe & Nantwich£483
Fit or replace an unvented hot water cylinder near Dacorum£573
Fit or replace an unvented hot water cylinder near Derby£457
Fit or replace an unvented hot water cylinder near Doncaster£493
Fit or replace an unvented hot water cylinder near Dover£475
Fit or replace an unvented hot water cylinder near Dudley£481
Fit or replace an unvented hot water cylinder near Dumfries & Galloway£511
Fit or replace an unvented hot water cylinder near Dundee£549
Fit or replace an unvented hot water cylinder near East Ayrshire£423
Fit or replace an unvented hot water cylinder near East Devon£495
Fit or replace an unvented hot water cylinder near East Dunbartonshire£567
Fit or replace an unvented hot water cylinder near East Hampshire£553
Fit or replace an unvented hot water cylinder near East Hertfordshire£569
Fit or replace an unvented hot water cylinder near East Lindsey£451
Fit or replace an unvented hot water cylinder near East Riding£395
Fit or replace an unvented hot water cylinder near Eastleigh£565
Fit or replace an unvented hot water cylinder near Edinburgh£539
Fit or replace an unvented hot water cylinder near Elmbridge£591
Fit or replace an unvented hot water cylinder near Epping Forest£591
Fit or replace an unvented hot water cylinder near Erewash£463
Fit or replace an unvented hot water cylinder near Exeter£513
Fit or replace an unvented hot water cylinder near Falkirk£555
Fit or replace an unvented hot water cylinder near Fife£541
Fit or replace an unvented hot water cylinder near Flintshire£457
Fit or replace an unvented hot water cylinder near Gateshead£525
Fit or replace an unvented hot water cylinder near Gedling£473
Fit or replace an unvented hot water cylinder near Glasgow£559
Fit or replace an unvented hot water cylinder near Gloucester£637
Fit or replace an unvented hot water cylinder near Guildford£603
Fit or replace an unvented hot water cylinder near Gwynedd£453
Fit or replace an unvented hot water cylinder near Halton£487
Fit or replace an unvented hot water cylinder near Harrogate£463
Fit or replace an unvented hot water cylinder near Havant & Waterloo£537
Fit or replace an unvented hot water cylinder near Highland£645
Fit or replace an unvented hot water cylinder near Horsham£549
Fit or replace an unvented hot water cylinder near Huntingdonshire£563
Fit or replace an unvented hot water cylinder near Ipswich£631
Fit or replace an unvented hot water cylinder near Isle of Wight£533
Fit or replace an unvented hot water cylinder near Kings Lynn & West Norfolk£525
Fit or replace an unvented hot water cylinder near Kingston-upon-Hull£397
Fit or replace an unvented hot water cylinder near Kirklees£469
Fit or replace an unvented hot water cylinder near Knowsley£481
Fit or replace an unvented hot water cylinder near Lancaster£531
Fit or replace an unvented hot water cylinder near Leeds£467
Fit or replace an unvented hot water cylinder near Leicester£465
Fit or replace an unvented hot water cylinder near Lisburn£449
Fit or replace an unvented hot water cylinder near Liverpool£479
Fit or replace an unvented hot water cylinder near London£587
Fit or replace an unvented hot water cylinder near Luton£581
Fit or replace an unvented hot water cylinder near Macclesfield£493
Fit or replace an unvented hot water cylinder near Maidstone£523
Fit or replace an unvented hot water cylinder near Manchester£489
Fit or replace an unvented hot water cylinder near Mid Bedfordshire£567
Fit or replace an unvented hot water cylinder near Mid Sussex£561
Fit or replace an unvented hot water cylinder near Middlesbrough£505
Fit or replace an unvented hot water cylinder near Milton Keynes£573
Fit or replace an unvented hot water cylinder near Neath Port Talbot£479
Fit or replace an unvented hot water cylinder near New Forest£553
Fit or replace an unvented hot water cylinder near Newbury£561
Fit or replace an unvented hot water cylinder near Newcastle-under-Lyme£465
Fit or replace an unvented hot water cylinder near Newcastle-upon-Tyne£527
Fit or replace an unvented hot water cylinder near Newport£475
Fit or replace an unvented hot water cylinder near North Ayrshire£459
Fit or replace an unvented hot water cylinder near North East Lincolnshire£495
Fit or replace an unvented hot water cylinder near North Hertfordshire£571
Fit or replace an unvented hot water cylinder near North Lanarkshire£561
Fit or replace an unvented hot water cylinder near North Lincolnshire£451
Fit or replace an unvented hot water cylinder near North Somerset£513
Fit or replace an unvented hot water cylinder near North Tyneside£521
Fit or replace an unvented hot water cylinder near North Wiltshire£617
Fit or replace an unvented hot water cylinder near Northampton£559
Fit or replace an unvented hot water cylinder near Norwich£525
Fit or replace an unvented hot water cylinder near Nottingham£465
Fit or replace an unvented hot water cylinder near Nuneaton & Bedworth£473
Fit or replace an unvented hot water cylinder near Oldham£493
Fit or replace an unvented hot water cylinder near Oxford£583
Fit or replace an unvented hot water cylinder near Pembrokeshire£407
Fit or replace an unvented hot water cylinder near Perth & Kinross£547
Fit or replace an unvented hot water cylinder near Peterborough£575
Fit or replace an unvented hot water cylinder near Plymouth£497
Fit or replace an unvented hot water cylinder near Poole£555
Fit or replace an unvented hot water cylinder near Portsmouth£533
Fit or replace an unvented hot water cylinder near Powys£605
Fit or replace an unvented hot water cylinder near Preston£489
Fit or replace an unvented hot water cylinder near Reading£599
Fit or replace an unvented hot water cylinder near Redcar & Cleveland£495
Fit or replace an unvented hot water cylinder near Reigate & Banstead£585
Fit or replace an unvented hot water cylinder near Renfrewshire£549
Fit or replace an unvented hot water cylinder near Rhondda, Cynon, Taff£455
Fit or replace an unvented hot water cylinder near Rochdale£495
Fit or replace an unvented hot water cylinder near Rochester-upon-Medway£565
Fit or replace an unvented hot water cylinder near Rotherham£481
Fit or replace an unvented hot water cylinder near Salford£489
Fit or replace an unvented hot water cylinder near Salisbury£513
Fit or replace an unvented hot water cylinder near Sandwell£479
Fit or replace an unvented hot water cylinder near Scarborough£533
Fit or replace an unvented hot water cylinder near Scottish Borders£765
Fit or replace an unvented hot water cylinder near Sefton£485
Fit or replace an unvented hot water cylinder near Sevenoaks£547
Fit or replace an unvented hot water cylinder near Sheffield£489
Fit or replace an unvented hot water cylinder near Slough£591
Fit or replace an unvented hot water cylinder near Solihull£479
Fit or replace an unvented hot water cylinder near South Ayrshire£463
Fit or replace an unvented hot water cylinder near South Bedfordshire£577
Fit or replace an unvented hot water cylinder near South Cambridgeshire£547
Fit or replace an unvented hot water cylinder near South Gloucestershire£529
Fit or replace an unvented hot water cylinder near South Kesteven£545
Fit or replace an unvented hot water cylinder near South Lanarkshire£537
Fit or replace an unvented hot water cylinder near South Oxfordshire£583
Fit or replace an unvented hot water cylinder near South Somerset£529
Fit or replace an unvented hot water cylinder near South Tyneside£523
Fit or replace an unvented hot water cylinder near Southampton£559
Fit or replace an unvented hot water cylinder near Southend-on-Sea£511
Fit or replace an unvented hot water cylinder near St Albans£589
Fit or replace an unvented hot water cylinder near St Helens£479
Fit or replace an unvented hot water cylinder near Stafford£489
Fit or replace an unvented hot water cylinder near Stockport£497
Fit or replace an unvented hot water cylinder near Stockton-on-Tees£507
Fit or replace an unvented hot water cylinder near Stoke-on-Trent£465
Fit or replace an unvented hot water cylinder near Stratford-on-Avon£503
Fit or replace an unvented hot water cylinder near Stroud£585
Fit or replace an unvented hot water cylinder near Suffolk Coastal£671
Fit or replace an unvented hot water cylinder near Sunderland£523
Fit or replace an unvented hot water cylinder near Swale£503
Fit or replace an unvented hot water cylinder near Swansea£465
Fit or replace an unvented hot water cylinder near Tameside£491
Fit or replace an unvented hot water cylinder near Teignbridge£505
Fit or replace an unvented hot water cylinder near Tendring£591
Fit or replace an unvented hot water cylinder near Test Valley£539
Fit or replace an unvented hot water cylinder near Thamesdown£625
Fit or replace an unvented hot water cylinder near Thanet£529
Fit or replace an unvented hot water cylinder near The Wrekin£505
Fit or replace an unvented hot water cylinder near Thurrock£535
Fit or replace an unvented hot water cylinder near Torbay£501
Fit or replace an unvented hot water cylinder near Trafford£499
Fit or replace an unvented hot water cylinder near Vale of Glamorgan£469
Fit or replace an unvented hot water cylinder near Vale of White Horse£595
Fit or replace an unvented hot water cylinder near Vale Royal£453
Fit or replace an unvented hot water cylinder near Wakefield£477
Fit or replace an unvented hot water cylinder near Walsall£479
Fit or replace an unvented hot water cylinder near Warrington£499
Fit or replace an unvented hot water cylinder near Warwick£489
Fit or replace an unvented hot water cylinder near Waveney£511
Fit or replace an unvented hot water cylinder near Waverley£593
Fit or replace an unvented hot water cylinder near Wealden£543
Fit or replace an unvented hot water cylinder near West Lancashire£485
Fit or replace an unvented hot water cylinder near West Lothian£567
Fit or replace an unvented hot water cylinder near West Wiltshire£617
Fit or replace an unvented hot water cylinder near Wigan£485
Fit or replace an unvented hot water cylinder near Windsor & Maidenhead£589
Fit or replace an unvented hot water cylinder near Wirral£475
Fit or replace an unvented hot water cylinder near Wokingham£591
Fit or replace an unvented hot water cylinder near Wolverhampton£483
Fit or replace an unvented hot water cylinder near Wrexham Maelor£533
Fit or replace an unvented hot water cylinder near Wychavon£533
Fit or replace an unvented hot water cylinder near Wycombe£607
Fit or replace an unvented hot water cylinder near York£459