System Boiler Installation Cost 2026 (UK)
A system boiler installation costs £1,900–£3,500 supplied and fitted in 2026 for a like-for-like swap, with larger outputs and a new hot-water cylinder pushing toward the top of the range. A system boiler keeps a cylinder but drops the loft feed tanks, making it the natural choice for homes with more than one bathroom or high simultaneous hot-water demand. Here is what a system boiler costs in 2026, how it compares to a combi, and the factors that move a quote.
2026 system boiler installation costs
| Job | Typical price (2026) | Time |
|---|---|---|
| System boiler swap (like-for-like, 18–24kW) | £1,900–£2,800 | 1 day |
| System boiler swap (28–35kW, larger home) | £2,400–£3,500 | 1–1.5 days |
| New hot-water cylinder (unvented) | +£800–£1,600 | +0.5 day |
| Convert regular to system boiler | £2,600–£4,000 | 1–2 days |
| System filter & power flush | +£400–£700 | +0.5 day |
System boiler vs combi: which should you fit?
A combi heats water on demand with no cylinder — cheapest to fit and ideal for flats and smaller homes with one bathroom. A system boiler stores hot water in a cylinder, so it can serve several taps and showers at once without the flow rate collapsing. If you have two or more bathrooms, or a large household, a system boiler is usually the better choice despite the cylinder taking up space.
What moves a system boiler quote
1. Output (kW)
Bigger homes with more radiators need a higher-output boiler, which costs more to buy. Sizing should be done on a heat-loss basis, not guesswork.
2. Cylinder
Reusing a sound cylinder keeps the price down; a new unvented cylinder adds £800–£1,600 but gives mains-pressure hot water to every tap.
3. System condition
An old, sludgy system often needs a power flush and a magnetic filter to protect the new boiler and keep the warranty valid.
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