The cost of unvented cylinder installation in London is usually £2,200 to £4,000 for a standard supply-and-fit job. UK-wide guides put the typical all-in cost at roughly £1,800 to £3,500. London quotes often land higher because of labour rates, parking and access. The cylinder itself is about £500 to £1,200 for most homes. Labour by a G3-qualified engineer is about £600 to £1,500. Swapping a vented system for an unvented one, or moving the cylinder, adds to the bill.
That range is a planning figure, not a fixed price. Below, you will see what drives the cost, how size and brand change it, what extras to expect, and how to get a fair quote.
How much does unvented cylinder installation cost in London?
A typical London job costs £2,200 to £4,000 fitted. This is my planning estimate. It starts from UK-wide guides and allows for higher London labour and access costs.
Published UK sources give these figures:
- Cylinder unit: about £700 to £1,800 in one 2026 guide, and about £500 to £1,200+ in another, depending on size and brand.
- Labour by a G3-qualified engineer: about £600 to £1,500.
- All-in for a standard installation: about £1,800 to £3,500.
- Another guide lists fitted unvented cylinders at £900 to £3,000 across the UK, before VAT.
The gap between sources is large. That is normal. It comes from different cylinder sizes, brands, and how much extra pipework is needed.
Why London prices are higher
London jobs often cost more for four simple reasons:
- Labour rates are higher than the UK average.
- Parking and congestion add time and sometimes extra charges.
- Access can be harder in flats, terraced houses and Victorian homes with narrow stairs.
- Demand is high for G3 engineers, especially for urgent jobs.
A quote from a small local firm may differ from a large national company. Compare at least three.
What affects the price of an unvented cylinder?
Five things drive most of the cost: cylinder size, brand and material, the type of swap, pipework changes, and extras like a new discharge route.
1. Cylinder size
Bigger cylinders cost more to buy and are heavier to fit. UK guides give these rough supply prices:
| Cylinder size | Typical supply price (UK) | Often suits |
|---|---|---|
| 150 litre | £500 to £750 | 1 to 2 bed flat or small house |
| 210 litre | £650 to £950 | 3 to 4 people, 2 bathrooms |
| 250 litre and above | £850 to £1,200+ | Larger homes, 3+ bathrooms |
One guide calls 210 litres the most popular size in UK homes. When in doubt, many installers suggest going up one size. The extra cost is small compared with running out of hot water.
2. Brand and material
Stainless steel cylinders usually cost more than enamel-lined steel, but they resist corrosion well. Well-known names include Megaflo (Heatrae Sadia), Gledhill, Telford, Joule, Albion and Kingspan. Many people say “Megaflo” when they mean any unvented cylinder. Ask what warranty each model comes with, and whether it needs annual servicing to stay valid.
3. Type of installation
- Like-for-like swap (old unvented for new unvented, same spot): the cheapest job. One guide puts labour at £400 to £700 for a one-day swap.
- Vented to unvented conversion: costs more and takes longer. The old tank and loft header tank must be removed and pipework changed.
- Moving the cylinder: adds pipework, floor work and time.
- New heating system with a cylinder: priced as a larger project, not just a cylinder fit.
4. Pipework and water supply
An unvented cylinder needs a good mains supply. If your incoming pipe is old lead or narrow, you may need a new supply pipe. That can add hundreds of pounds. Ask your installer to test pressure and flow rate (in litres per minute) before quoting.
5. Safety parts and discharge pipe
Every unvented cylinder needs safety devices. These include an expansion vessel, a pressure reducing valve, a temperature and pressure relief valve, and a tundish with a discharge pipe. The discharge pipe must run safely to a visible spot. In flats or tight spaces, finding a compliant route can raise the cost.
Cost breakdown: what you are actually paying for
Your quote should cover the cylinder, labour, safety parts, certification and old-tank removal.
| Item | Typical cost range |
|---|---|
| Cylinder unit | £500 to £1,800 |
| G3 engineer labour (1 to 2 days) | £600 to £1,500 |
| Safety kit and fittings (if not included) | Often included in the cylinder pack, ask to confirm |
| Removing and disposing of old cylinder or tank | Often included, sometimes extra |
| Building Regulations notification or certificate | Usually included by the installer, ask to confirm |
| Extra pipework, new supply pipe, new discharge route | Priced per job |
Day rates for fitting unvented cylinders in some UK areas are around £240 to £290, but London rates are usually higher. Labour is only part of the bill, so do not use day rates alone to judge a quote.
Hidden costs to ask about
- Scaffold or loft access for removing a loft tank
- Draining and flushing the heating system
- New immersion heater or controls
- Making good plasterboard or flooring
- Extended warranty or first-year service
- Parking permits or congestion charges
Unvented vs vented cylinder: cost comparison
Unvented cylinders cost more upfront, but they give mains-pressure hot water and free up loft space.
| Feature | Vented (gravity) | Unvented (mains pressure) |
|---|---|---|
| Typical fitted cost (UK guide) | £750 to £1,400 | £900 to £3,000 |
| Water pressure | Low, depends on tank height | Strong, from the mains |
| Needs loft tank | Yes | No |
| Installer qualification | Standard plumbing | G3 qualified |
| Annual servicing | Not usually needed | Recommended |
| Best for | Low budgets, low demand | Multiple bathrooms, power showers |
For homes with two or more bathrooms, the pressure boost is often worth it. For a small flat with one shower and low use, a vented cylinder or a combi boiler may be enough.
Unvented cylinder vs combi boiler
A combi boiler heats water on demand and has no cylinder. It saves space. But if two taps run at once, flow can drop. An unvented cylinder with a system boiler stores hot water, so several outlets can run together. A combi to system boiler switch plus a cylinder costs much more than a cylinder swap alone, so ask for a full price breakdown.
Is an unvented cylinder worth it?
Yes, if you have more than one bathroom or want stronger showers. No, if your supply is weak or space and budget are tight.
Pros
- Strong, balanced pressure at taps and showers
- No loft tank, so less risk of freezing or leaks in the loft
- Fast refill and good for busy households
- Works with system boilers, solar thermal and many heat pumps (check coil size)
Cons
- Higher upfront cost
- Needs a G3-qualified installer and regular servicing
- Depends on good mains pressure and flow
- Heavy, so floor strength matters
One point to check early: if you plan to add a heat pump later, ask for a cylinder with a coil sized for it. Fitting a standard cylinder now and replacing it in a few years would cost you twice.
G3 rules: why the installer matters
Unvented cylinders must be installed by someone who holds a G3 qualification, and the work must comply with Building Regulations Part G.
The UK government publishes guidance on hot water systems under Building Regulations. In plain terms, this means:
- The installer needs a G3 unvented hot water qualification. It is separate from a general plumbing or Gas Safe card.
- The installation must be notified to Building Control, or certified through a competent person scheme.
- You should receive a commissioning record and a Building Regulations compliance certificate.
- Keep these papers. You will need them if you sell, rent out or claim on the warranty.
Can you fit one yourself? Legally you can notify Building Control for your own work, but unvented systems store water at high pressure and temperature. Mistakes can be dangerous. Most manufacturers also void the warranty if a qualified person does not install it. For most homeowners, a G3 engineer is the safe choice.
Landlords: a hot water system with safety defects can create legal risks. Ask your engineer to supply the certificate and keep a service record.
How long does installation take?
Most unvented cylinder installations take one to two days.
A like-for-like swap can be done in a day. A vented to unvented conversion often takes longer. Here is the typical process:
- Survey and pressure test. The engineer checks mains pressure, flow rate, cylinder location and discharge route.
- Quote and agree the plan. You approve size, brand and extras.
- Drain and remove the old cylinder and, if needed, the loft tanks.
- Position and connect the new cylinder. The engineer fits the expansion vessel, valves and tundish.
- Run the discharge pipe to a safe, visible point.
- Fill, test and commission. Pressure, temperature and safety valves are checked.
- Notify Building Control and hand over paperwork. You get the certificate, manuals and warranty details.
Book early in winter. Emergency replacements in London can cost more and have less choice of models.
Running costs, servicing and lifespan
Expect to pay for an annual service, and expect a quality cylinder to last 20 years or more with care. Lifespan depends on water hardness, material and servicing, so treat any single figure as a guide.
Annual servicing normally includes checking the expansion vessel, pressure valves, tundish and discharge pipe. Hard water areas, which includes much of London, can cause scale. This can affect the heating coil and valves, so a service matters.
Standing heat loss also affects running costs. A well-insulated cylinder wastes less heat. Pick a model with good insulation and ask for the heat loss figure on the data sheet.
Common faults to watch for:
- Water dripping from the discharge pipe, often a failing valve or an expansion vessel with low air charge
- No hot water, which may point to a faulty thermostat or immersion heater
- Pressure loss, sometimes from a faulty expansion vessel
How to save money on cylinder installation
Get three written quotes, choose the right size, and avoid last-minute emergency work.
- Compare quotes line by line: cylinder model, warranty, labour, extras, certification.
- Do not pick the cheapest if it excludes the discharge pipe, old-tank removal or paperwork.
- Choose the right size. Too big costs more to buy and run. Too small leaves you short of hot water.
- Check if your supplier offers a fixed price rather than an hourly rate.
- Ask whether your cylinder can be paired with a future heat pump.
- Grants usually apply to heat pump systems, not standard cylinder swaps. Check the current Boiler Upgrade Scheme rules on GOV.UK before you rely on any grant.
- VAT rules for energy-saving work can change. Ask your installer what applies to your job and check GOV.UK.
Common mistakes London homeowners make
- Buying a cylinder online and then finding no G3 installer will fit it
- Ignoring mains pressure and flow tests
- Choosing a size by price instead of the number of bathrooms and occupants
- Skipping the building regulations certificate
- Not asking who handles the discharge pipe route
- Forgetting that the floor or cupboard must carry the weight of a full cylinder
How to choose a London installer
Look for these signs:
- A current G3 certificate, and Gas Safe registration if gas work is involved
- A written quote that lists the cylinder model, warranty and exclusions
- Clear details on Building Regulations certification
- Insurance and local reviews
- Clear answers about servicing and aftercare
If you want a quote, share your property type, number of bathrooms, current system and photos of your current cylinder. This helps an engineer give a closer price without a wasted visit.
Frequently asked questions
How much does it cost to replace a hot water cylinder in London?
A standard unvented cylinder replacement in London usually costs about £2,200 to £4,000 fitted. A like-for-like swap is often cheaper, and a vented to unvented conversion costs more.
How long does it take to fit an unvented cylinder?
Most jobs take one to two days. A simple swap may take one day, while conversions and pipework changes take longer.
What size unvented cylinder do I need?
A 150 litre cylinder suits small homes, and 210 litres suits many 3 to 4 person homes with two bathrooms. Larger homes often need 250 litres or more.
Do I need Building Regulations approval?
Yes. An unvented cylinder installation must be notified to Building Control or certified by a competent person scheme. Your installer should give you a certificate.
Can any plumber install an unvented cylinder?
No. The installer must hold a G3 unvented hot water qualification. A general plumbing or Gas Safe qualification is not enough on its own.
Do unvented cylinders need servicing every year?
Manufacturers and installers recommend an annual service. This keeps safety valves, the expansion vessel and the discharge pipe working.
Is an unvented cylinder better than a combi boiler?
It depends on your home. An unvented cylinder suits busy homes with several bathrooms. A combi boiler suits small homes with low hot water demand.
Is an unvented cylinder worth the extra cost?
Usually yes for homes with two or more bathrooms, because of better pressure and no loft tank. For a small flat with low use, it may not be.
Can I replace a vented cylinder with an unvented one?
Yes, but it costs more and takes longer. The loft tanks and old pipework usually need to be removed or changed.
How long do unvented cylinders last?
With good servicing, many last 20 years or more. Water quality and the cylinder material affect lifespan, and warranties vary by brand.
Conclusion
The cost of unvented cylinder installation in London depends mostly on size, installation type and access. Plan for about £2,200 to £4,000 for a standard job, and ask each installer to list the cylinder, labour, safety kit, discharge pipe and certification separately. Choose a G3-qualified engineer, keep your certificate, and book an annual service.
Ready to compare? Send your property details and photos to get a clear, itemised quote from a London G3 engineer.