System Boiler Installation London
For homes with two or more bathrooms, a system boiler with an unvented cylinder delivers strong, consistent hot water to every tap at once — something a combi boiler can't reliably do. Fixed pricing from £2,499, confirmed after a free assessment.
How much does system boiler installation cost in London?
System boiler installation with an unvented cylinder starts from £2,499, including the boiler, cylinder, discharge pipework and Gas Safe certificate. Other London quotes we've seen range anywhere from £1,700 to £5,500 without saying why — the real driver is cylinder size and how much of your existing pipework needs altering, not just the boiler brand. We confirm your exact price with a free assessment before you commit to anything, so you know the real number, not a guess.
System Boiler or Combi? How to Actually Decide
Most installer sites push combi boilers because they're a simpler sale. The honest answer depends entirely on how many bathrooms you have and whether they'd ever be used at the same time.
| Question | Combi Boiler | System Boiler + Cylinder |
|---|---|---|
| Bathrooms | 1, or 2 used at different times | 2 or more, especially used simultaneously |
| Hot water delivery | Heated on demand, unlimited but pressure drops if shared | Stored under pressure, multiple outlets run together |
| Space needed | Boiler only, fits a kitchen cupboard | Boiler plus cylinder, usually an airing cupboard |
| Typical property | Flats, 1-2 bed homes | 3+ bed houses, HMOs, larger family homes |
| Typical price | £1,399 – £2,699 | £2,499+ |
What's Included in Your System Boiler Installation
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Boiler and unvented cylinder, correctly sized
We size both to your actual bathroom count and hot water demand, not a generic default.
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Discharge pipework to outside
Required by building regulations for unvented systems, routed and fitted as part of the job.
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Building Control notification
We handle the required notification to your local authority Building Control department before work starts.
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System flush, magnetic filter & scale reducer
Protects both the boiler and cylinder from London's hard water, included as standard.
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Gas Safe certificate, same day
Issued before the engineer leaves, along with warranty registration for your boiler and cylinder.
⚠ Why this job costs more than a combi swap
Unvented cylinder installation is legally required to be carried out by an engineer specifically qualified in unvented hot water systems, separate from standard Gas Safe registration, with mandatory notification to Building Control. That additional qualification, safety pipework and cylinder cost is reflected in the price — it's not simply a bigger boiler.
Find Your Perfect System Boiler Size
Answer 3 quick questions about your home and we'll recommend the right boiler output and cylinder size — then confirm the exact fit with a free assessment.
Who Actually Needs a System Boiler
3+ bedroom houses, 2+ bathrooms
Common across Ealing, Harrow, Wimbledon and Croydon family homes where morning showers overlap.
Multiple tenants, shared bathrooms
Shared houses in areas like Clapham and Shoreditch see heavy simultaneous hot water demand a combi can't handle well.
Townhouses with en-suites
Georgian and Victorian townhouses across Richmond, Kensington and Greenwich often have several bathrooms added over the years.
Homes adding a bathroom or loft en-suite
If an extension is adding a third bathroom, it's worth reassessing whether your existing combi will still cope.
System Boiler Installation — Common Questions
Do I need a system boiler or a combi boiler?
If your home has two or more bathrooms that might be used at the same time, a system boiler with a stored cylinder is usually the better choice, since it can supply multiple showers simultaneously without a drop in pressure. A combi boiler heats water on demand and suits homes with one bathroom, or two bathrooms rarely used together.
What is an unvented cylinder and do I need one?
An unvented cylinder stores hot water under mains pressure, without needing a cold water tank in the loft. It's required alongside a system boiler to deliver strong, consistent pressure to multiple bathrooms at once. Almost all modern system boiler installations in London use an unvented cylinder rather than the older vented tank-and-cylinder setup.
Is a system boiler installation regulated differently to a combi?
Yes. Alongside standard Gas Safe registration for the gas work, installing an unvented hot water cylinder requires specific qualification in unvented cylinder systems, and your local authority Building Control department must be notified before installation, since safety valves and discharge pipework are involved.
Do you offer same day quotes for system boiler installation?
Yes. Message us your property details on WhatsApp and we'll confirm a firm price and installation date, subject to a quick assessment of your existing pipework and cylinder space.
Get a Free System Boiler Assessment
Tell us your bathroom count and property type on WhatsApp and we'll confirm the right cylinder size and firm price before you commit to anything.
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