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

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;

Job Estimate
Cost to replace a hot water immersion heater £275
Cost to fit underfloor heating £250
Cost to replace a vented hot water cylinder £330
Cost to replace a heating programmer £180
Cost to powerflush a central heating system £500 Visit
New combi or system boiler installation – like for like replacement £500
Cost to install a ground source heat pump £3750
Cost to fix a boiler fault error code £85
Cost to replace an unvented hot water cylinder, e.g., Megaflo £305
Cost to fit thermostatic radiator valves (TRVs) £94
Cost to fit smart heating controls £100
Cost to fit a radiator £80
Boiler service cost £90
Boiler repair costs (e.g. pump, diverter valve or heat exchanger) £333
Cost to install an air source heat pump £556
Replacement of a vented system £580

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£565
Fit or replace an unvented hot water cylinder near Amber Valley£485
Fit or replace an unvented hot water cylinder near Angus£545
Fit or replace an unvented hot water cylinder near Arun£551
Fit or replace an unvented hot water cylinder near Ashfield£481
Fit or replace an unvented hot water cylinder near Aylesbury Vale£567
Fit or replace an unvented hot water cylinder near Barnsley£471
Fit or replace an unvented hot water cylinder near Basildon£533
Fit or replace an unvented hot water cylinder near Basingstoke & Deane£551
Fit or replace an unvented hot water cylinder near Bassetlaw£495
Fit or replace an unvented hot water cylinder near Bath & North East Somerset£525
Fit or replace an unvented hot water cylinder near Bedford£565
Fit or replace an unvented hot water cylinder near Belfast£429
Fit or replace an unvented hot water cylinder near Birmingham£469
Fit or replace an unvented hot water cylinder near Blackburn£479
Fit or replace an unvented hot water cylinder near Blackpool£491
Fit or replace an unvented hot water cylinder near Bolton£501
Fit or replace an unvented hot water cylinder near Bournemouth£547
Fit or replace an unvented hot water cylinder near Bracknell Forest£579
Fit or replace an unvented hot water cylinder near Bradford£473
Fit or replace an unvented hot water cylinder near Braintree£521
Fit or replace an unvented hot water cylinder near Breckland£489
Fit or replace an unvented hot water cylinder near Bridgend£457
Fit or replace an unvented hot water cylinder near Brighton£533
Fit or replace an unvented hot water cylinder near Bristol£511
Fit or replace an unvented hot water cylinder near Broadland£539
Fit or replace an unvented hot water cylinder near Broxtowe£479
Fit or replace an unvented hot water cylinder near Bury£495
Fit or replace an unvented hot water cylinder near Caerphilly£457
Fit or replace an unvented hot water cylinder near Calderdale£465
Fit or replace an unvented hot water cylinder near Cambridge£555
Fit or replace an unvented hot water cylinder near Canterbury£495
Fit or replace an unvented hot water cylinder near Cardiff£469
Fit or replace an unvented hot water cylinder near Carmarthenshire£403
Fit or replace an unvented hot water cylinder near Charnwood£465
Fit or replace an unvented hot water cylinder near Chelmsford£523
Fit or replace an unvented hot water cylinder near Cheltenham£625
Fit or replace an unvented hot water cylinder near Cherwell£559
Fit or replace an unvented hot water cylinder near Chester£443
Fit or replace an unvented hot water cylinder near Colchester£515
Fit or replace an unvented hot water cylinder near Conway£413
Fit or replace an unvented hot water cylinder near Coventry£471
Fit or replace an unvented hot water cylinder near Crewe & Nantwich£473
Fit or replace an unvented hot water cylinder near Dacorum£565
Fit or replace an unvented hot water cylinder near Derby£465
Fit or replace an unvented hot water cylinder near Doncaster£493
Fit or replace an unvented hot water cylinder near Dover£473
Fit or replace an unvented hot water cylinder near Dudley£471
Fit or replace an unvented hot water cylinder near Dumfries & Galloway£509
Fit or replace an unvented hot water cylinder near Dundee£553
Fit or replace an unvented hot water cylinder near East Ayrshire£385
Fit or replace an unvented hot water cylinder near East Devon£499
Fit or replace an unvented hot water cylinder near East Dunbartonshire£573
Fit or replace an unvented hot water cylinder near East Hampshire£543
Fit or replace an unvented hot water cylinder near East Hertfordshire£559
Fit or replace an unvented hot water cylinder near East Lindsey£443
Fit or replace an unvented hot water cylinder near East Riding£397
Fit or replace an unvented hot water cylinder near Eastleigh£565
Fit or replace an unvented hot water cylinder near Edinburgh£517
Fit or replace an unvented hot water cylinder near Elmbridge£589
Fit or replace an unvented hot water cylinder near Epping Forest£591
Fit or replace an unvented hot water cylinder near Erewash£471
Fit or replace an unvented hot water cylinder near Exeter£519
Fit or replace an unvented hot water cylinder near Falkirk£555
Fit or replace an unvented hot water cylinder near Fife£527
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£475
Fit or replace an unvented hot water cylinder near Glasgow£563
Fit or replace an unvented hot water cylinder near Gloucester£649
Fit or replace an unvented hot water cylinder near Guildford£597
Fit or replace an unvented hot water cylinder near Gwynedd£469
Fit or replace an unvented hot water cylinder near Halton£477
Fit or replace an unvented hot water cylinder near Harrogate£453
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£541
Fit or replace an unvented hot water cylinder near Huntingdonshire£547
Fit or replace an unvented hot water cylinder near Ipswich£611
Fit or replace an unvented hot water cylinder near Isle of Wight£529
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£461
Fit or replace an unvented hot water cylinder near Knowsley£469
Fit or replace an unvented hot water cylinder near Lancaster£519
Fit or replace an unvented hot water cylinder near Leeds£459
Fit or replace an unvented hot water cylinder near Leicester£469
Fit or replace an unvented hot water cylinder near Lisburn£427
Fit or replace an unvented hot water cylinder near Liverpool£467
Fit or replace an unvented hot water cylinder near London£583
Fit or replace an unvented hot water cylinder near Luton£579
Fit or replace an unvented hot water cylinder near Macclesfield£489
Fit or replace an unvented hot water cylinder near Maidstone£515
Fit or replace an unvented hot water cylinder near Manchester£483
Fit or replace an unvented hot water cylinder near Mid Bedfordshire£561
Fit or replace an unvented hot water cylinder near Mid Sussex£553
Fit or replace an unvented hot water cylinder near Middlesbrough£493
Fit or replace an unvented hot water cylinder near Milton Keynes£567
Fit or replace an unvented hot water cylinder near Neath Port Talbot£473
Fit or replace an unvented hot water cylinder near New Forest£543
Fit or replace an unvented hot water cylinder near Newbury£553
Fit or replace an unvented hot water cylinder near Newcastle-under-Lyme£451
Fit or replace an unvented hot water cylinder near Newcastle-upon-Tyne£527
Fit or replace an unvented hot water cylinder near Newport£471
Fit or replace an unvented hot water cylinder near North Ayrshire£453
Fit or replace an unvented hot water cylinder near North East Lincolnshire£513
Fit or replace an unvented hot water cylinder near North Hertfordshire£565
Fit or replace an unvented hot water cylinder near North Lanarkshire£565
Fit or replace an unvented hot water cylinder near North Lincolnshire£447
Fit or replace an unvented hot water cylinder near North Somerset£501
Fit or replace an unvented hot water cylinder near North Tyneside£523
Fit or replace an unvented hot water cylinder near North Wiltshire£625
Fit or replace an unvented hot water cylinder near Northampton£549
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£465
Fit or replace an unvented hot water cylinder near Oldham£489
Fit or replace an unvented hot water cylinder near Oxford£567
Fit or replace an unvented hot water cylinder near Pembrokeshire£413
Fit or replace an unvented hot water cylinder near Perth & Kinross£545
Fit or replace an unvented hot water cylinder near Peterborough£553
Fit or replace an unvented hot water cylinder near Plymouth£497
Fit or replace an unvented hot water cylinder near Poole£545
Fit or replace an unvented hot water cylinder near Portsmouth£531
Fit or replace an unvented hot water cylinder near Powys£621
Fit or replace an unvented hot water cylinder near Preston£497
Fit or replace an unvented hot water cylinder near Reading£581
Fit or replace an unvented hot water cylinder near Redcar & Cleveland£475
Fit or replace an unvented hot water cylinder near Reigate & Banstead£587
Fit or replace an unvented hot water cylinder near Renfrewshire£539
Fit or replace an unvented hot water cylinder near Rhondda, Cynon, Taff£435
Fit or replace an unvented hot water cylinder near Rochdale£489
Fit or replace an unvented hot water cylinder near Rochester-upon-Medway£565
Fit or replace an unvented hot water cylinder near Rotherham£479
Fit or replace an unvented hot water cylinder near Salford£483
Fit or replace an unvented hot water cylinder near Salisbury£507
Fit or replace an unvented hot water cylinder near Sandwell£467
Fit or replace an unvented hot water cylinder near Scarborough£489
Fit or replace an unvented hot water cylinder near Scottish Borders£745
Fit or replace an unvented hot water cylinder near Sefton£467
Fit or replace an unvented hot water cylinder near Sevenoaks£539
Fit or replace an unvented hot water cylinder near Sheffield£489
Fit or replace an unvented hot water cylinder near Slough£583
Fit or replace an unvented hot water cylinder near Solihull£469
Fit or replace an unvented hot water cylinder near South Ayrshire£459
Fit or replace an unvented hot water cylinder near South Bedfordshire£565
Fit or replace an unvented hot water cylinder near South Cambridgeshire£535
Fit or replace an unvented hot water cylinder near South Gloucestershire£519
Fit or replace an unvented hot water cylinder near South Kesteven£549
Fit or replace an unvented hot water cylinder near South Lanarkshire£557
Fit or replace an unvented hot water cylinder near South Oxfordshire£553
Fit or replace an unvented hot water cylinder near South Somerset£531
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£515
Fit or replace an unvented hot water cylinder near St Albans£585
Fit or replace an unvented hot water cylinder near St Helens£467
Fit or replace an unvented hot water cylinder near Stafford£477
Fit or replace an unvented hot water cylinder near Stockport£487
Fit or replace an unvented hot water cylinder near Stockton-on-Tees£497
Fit or replace an unvented hot water cylinder near Stoke-on-Trent£451
Fit or replace an unvented hot water cylinder near Stratford-on-Avon£497
Fit or replace an unvented hot water cylinder near Stroud£581
Fit or replace an unvented hot water cylinder near Suffolk Coastal£645
Fit or replace an unvented hot water cylinder near Sunderland£523
Fit or replace an unvented hot water cylinder near Swale£509
Fit or replace an unvented hot water cylinder near Swansea£461
Fit or replace an unvented hot water cylinder near Tameside£481
Fit or replace an unvented hot water cylinder near Teignbridge£509
Fit or replace an unvented hot water cylinder near Tendring£579
Fit or replace an unvented hot water cylinder near Test Valley£527
Fit or replace an unvented hot water cylinder near Thamesdown£625
Fit or replace an unvented hot water cylinder near Thanet£515
Fit or replace an unvented hot water cylinder near The Wrekin£513
Fit or replace an unvented hot water cylinder near Thurrock£535
Fit or replace an unvented hot water cylinder near Torbay£505
Fit or replace an unvented hot water cylinder near Trafford£489
Fit or replace an unvented hot water cylinder near Vale of Glamorgan£465
Fit or replace an unvented hot water cylinder near Vale of White Horse£575
Fit or replace an unvented hot water cylinder near Vale Royal£453
Fit or replace an unvented hot water cylinder near Wakefield£471
Fit or replace an unvented hot water cylinder near Walsall£467
Fit or replace an unvented hot water cylinder near Warrington£495
Fit or replace an unvented hot water cylinder near Warwick£481
Fit or replace an unvented hot water cylinder near Waveney£511
Fit or replace an unvented hot water cylinder near Waverley£575
Fit or replace an unvented hot water cylinder near Wealden£545
Fit or replace an unvented hot water cylinder near West Lancashire£475
Fit or replace an unvented hot water cylinder near West Lothian£555
Fit or replace an unvented hot water cylinder near West Wiltshire£625
Fit or replace an unvented hot water cylinder near Wigan£479
Fit or replace an unvented hot water cylinder near Windsor & Maidenhead£581
Fit or replace an unvented hot water cylinder near Wirral£461
Fit or replace an unvented hot water cylinder near Wokingham£583
Fit or replace an unvented hot water cylinder near Wolverhampton£469
Fit or replace an unvented hot water cylinder near Wrexham Maelor£571
Fit or replace an unvented hot water cylinder near Wychavon£535
Fit or replace an unvented hot water cylinder near Wycombe£593
Fit or replace an unvented hot water cylinder near York£461