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A new unvented hot water cylinder in London costs £1,495 to £2,845 fully fitted like-for-like: about £1,595 for 150 litres, £1,895 to £2,145 for 210 litres and £2,595 to £2,845 for 300 litres, including the G3 notification, commissioning and disposal. Converting a vented system with a loft tank starts at about £2,495; an annual service is £155.
| Job | London low | London typical | London high | UK typical | What moves the price |
|---|---|---|---|---|---|
| Unvented cylinder, like-for-like replacement, fully fitted | £1,495 | £2,095 | £2,845 | 150 to 300 litres; includes G3 notification, Benchmark commissioning and disposal; UK quotes run £900 to £3,500 with London 15 to 25 per cent above | |
| 150 to 210 litre cylinder | £1,595 | £1,895 | £2,145 | At 210 litres the spread is the brand | |
| 250 to 300 litre cylinder | £2,195 | £2,595 | £2,845 | A premium 300 litre cylinder is the top of the band | |
| Vented to unvented conversion | £2,495 | £2,495 | £2,495 | £2,150 | Published as a London starting price; removes the cold water tank from the loft; £1,300 to £3,000 across the UK |
| Annual unvented cylinder service (G3 check) | £155 | £155 | £155 | One published London price; an unserviced cylinder lasts 8 to 10 years in London water | |
| System boiler and unvented cylinder together | £4,200 | £5,100 | £6,000 | For a home with three or more bedrooms and two or more bathrooms |
Most London cylinder jobs are one of three things: a like-for-like swap of a failed unvented cylinder, a conversion from an old vented system with a cold water tank in the loft to an unvented cylinder fed from the mains, or a new cylinder fitted with a system boiler in a home with two or more bathrooms. Quotes are fully fitted and should include the Part G3 notification, the Benchmark commissioning record and disposal of the old cylinder.
An unvented cylinder holds hot water at mains pressure, so under Part G3 of the Building Regulations it must be installed and commissioned by a G3-qualified engineer and either notified to building control or self-certified through a competent-person scheme. The qualification is renewed every five years. Ask for the notification in the quote.
London water is hard, and a cylinder that is never serviced lasts eight to ten years here; an annual service is £155. Cheaper quotes exist, from £900, and £1,000 to £1,540 in south-west London, but check what they leave out. The only homeowner checks are the timer, the thermostat and the immersion heater switch; the valves on the cylinder are not for adjusting.
Prices last checked: September 2026. Based on the published 2026 cylinder price list of a London heating and plumbing firm, a west London installer's package prices, a UK cost guide and Checkatrade and aggregator snippets. PROS AI does not yet have enough completed cylinder jobs in London to publish its own averages.
£1,495 to £2,845 for an unvented cylinder fitted like-for-like: about £1,595 for 150 litres, £1,895 to £2,145 for 210 litres, £2,195 for 250 litres and £2,595 to £2,845 for 300 litres, with the brand setting the spread at each size. Those prices include the G3 notification, commissioning and disposal. Across the UK the same job runs £900 to £3,500, with London and the South East 15 to 25 per cent above.
Yes. Part G3 of the Building Regulations requires an unvented cylinder to be installed and commissioned by a G3-qualified operative, and the work to be notified to building control or self-certified through a competent-person scheme. The qualification is renewed every five years. A quote should say that G3 notification and Benchmark commissioning are included; if it does not, ask before you accept it.
The installer sizes it on bedrooms, bathrooms and how many showers run at once. London price lists cover 150, 210, 250 and 300 litres, and each step up adds £300 to £400 to the fitted price. A home with three or more bedrooms and two or more bathrooms is where installers quote a system boiler and cylinder together, at £4,200 to £6,000. Ask the engineer to size it in writing.
A conversion starts at about £2,495 in London and runs £1,300 to £3,000 across the UK. It removes the cold water tank from the loft and gives hot water at mains pressure. It makes most sense when the old cylinder or the loft tank needs replacing anyway, or as part of a system boiler installation, quoted at £4,200 to £6,000 for a home with two or more bathrooms.
Once a year; the published London price is £155. Unvented cylinders run at mains pressure, so the annual check is a safety check as well as maintenance and only a G3-qualified engineer should do it. In London's hard water a cylinder that is never serviced lasts eight to ten years. If you have a gas boiler, book the cylinder service on the same visit as the boiler service.
Written by Shay Hazan, PROS AI.
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