System Boiler Conversion London
Fed up with weak, shared pressure whenever two showers run at once? Converting from a combi to a system boiler with a stored cylinder fixes that permanently. From £3,500, including the cylinder.
What a System Boiler Conversion Actually Involves
A system boiler conversion means switching from your current combi, conventional, or back boiler setup to a system boiler paired with an unvented hot water cylinder. Unlike a like-for-like swap, this isn't just unit-for-unit — it involves running new pipework to wherever the cylinder is going, removing any redundant tanks if you're converting from an old gravity-fed system, and fitting the cylinder itself. That extra work is exactly why it costs more and takes longer than a straight combi replacement, and also why the result is genuinely different: strong, simultaneous hot water at every bathroom, not water heated on demand and shared across whatever's running.
How Much Does It Cost?
System boiler conversion in London starts from £3,500. Market rates for this exact job typically range from £3,200 to £5,500 depending on the source — again, a wide bracket that depends heavily on your specific pipework and cylinder location. Our starting price covers the boiler, an appropriately sized unvented cylinder, and the pipework needed for a standard conversion.
⚠ Why the price range is wider than a like-for-like swap
Conversion pricing depends heavily on how far the cylinder location is from the boiler, whether floors or walls need opening for new pipework, and the size of cylinder your household actually needs. Two homes on the same street can have genuinely different conversion costs. The £100 assessment visit is where we confirm all of this and give you a firm, final number before you commit — not a guess that changes once work starts.
Do You Actually Need a System Boiler Conversion?
This is worth being honest about before you spend the money. A conversion makes sense when:
| Signal | What It Means |
|---|---|
| Two bathrooms used at similar times | Combi pressure drops noticeably when both run — a real conversion case |
| Planning a bathroom or en-suite extension | Worth converting before the extension, not retrofitting after |
| Large family or shared household | Simultaneous demand is the main driver for needing stored hot water |
| Single bathroom, used one at a time | A combi replacement is usually the better value option, not a conversion |
If you're not sure which situation you're in, tell us your bathroom count and usage pattern on WhatsApp and we'll give you an honest answer — including if a straightforward like-for-like combi replacement would actually serve you just as well for less money.
Find Your Perfect System Boiler Size
Answer 3 quick questions about your home and we'll recommend the right boiler output and cylinder size for your conversion — then confirm the exact fit with a free assessment.
What's Included in Your Conversion
- ✓
New system boiler, correctly sized
Matched to your household's actual bathroom count and hot water demand.
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Unvented cylinder & discharge pipework
Sized appropriately for your home, with required safety pipework fitted to current building regulations.
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New pipework to the cylinder location
Routed with minimal disruption, confirmed during your assessment visit.
- ✓
Old tank & redundant pipework removal
If you're converting from an old gravity-fed system, we remove the loft tank and any pipework no longer needed.
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Building Control notification
Required for unvented cylinder installations — we handle this notification as part of the job.
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Gas Safe certificate, same day
Issued before the engineer leaves, along with warranty registration for both the boiler and cylinder.
Why Convert Instead of Sticking With a Combi
No shared flow between bathrooms
A cylinder stores water under pressure, so two showers running together both stay strong.
Built for bigger households
System boilers are designed for the higher simultaneous demand that combis simply weren't built to handle.
Works well with future extensions
If you're planning to add a bathroom later, converting now avoids a second disruptive job down the line.
Appeals to family buyers
Multiple-bathroom homes with genuinely strong simultaneous hot water are a real selling point in London's family housing market.
System Boiler Conversion — Common Questions
What is a system boiler conversion?
A system boiler conversion means changing from your current combi, conventional or back boiler setup to a system boiler paired with an unvented hot water cylinder. It involves new pipework to the cylinder location, removal of any old tanks, and fitting the cylinder itself, which is why it costs more and takes longer than a like-for-like combi swap.
Why would I convert from a combi to a system boiler?
The main reason is hot water pressure when more than one bathroom is used at the same time. A combi heats water on demand and its flow rate is shared across whatever's running, so two showers at once means both get weaker. A system boiler stores hot water under pressure in the cylinder, so multiple bathrooms can run together at full strength.
How long does a system boiler conversion take?
A system boiler conversion typically takes one to two days, depending on how much new pipework is needed and where the cylinder is being installed. This is longer than a like-for-like swap because it involves running new pipework rather than reconnecting to what's already there.
Where does the cylinder go in a system boiler conversion?
Most London homes use an airing cupboard, understairs cupboard, or a section of a loft with adequate access. We assess suitable locations during the free assessment visit and confirm what's realistic for your specific layout before quoting a final price.
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Book Your Free Conversion Assessment
Tell us your bathroom count and property type on WhatsApp and we'll confirm your exact conversion price with a £100 assessment visit.
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