--- title: "Combi Boiler vs System Boiler for Your Home" description: "Combi boiler vs system boiler: compare hot water demand, property size, cylinder space and running costs to pick the right boiler for your South London home." published: "2026-09-11T09:00:00Z" author: "Reion Miller" category: "Boiler Guides" content_type: "BlogPost" intent: "informational" business: "R.W. Miller Plumbing & Heating" gas_safe: "919881" service_area: "South London, Surrey" canonical: "https://rwmiller.com/blog/combi-boiler-vs-system-boiler/" markdown_url: "https://rwmiller.com/blog/combi-boiler-vs-system-boiler.md" --- # Combi Boiler vs System Boiler for Your Home > Combi boiler vs system boiler: compare hot water demand, property size, cylinder space and running costs to pick the right boiler for your South London home. Combi boiler vs system boiler: a combi heats water instantly from the mains with no cylinder, while a system boiler stores hot water in a cylinder to supply multiple bathrooms at once. If your boiler is old, unreliable or expensive to run, replacing it can make a noticeable difference to your home's heating and hot water. A combi boiler is often the first option homeowners consider, but a system boiler may be better for larger households. If you are also asking how much does a new boiler cost, the answer depends on the boiler type, brand, installation work and your home's requirements. ## Combi boiler vs system boiler: what's the difference? The main difference is how each boiler provides hot water. A combi boiler heats water directly from the mains when you turn on a tap. It does not need a separate hot water cylinder, making it a compact option. A system boiler heats water and stores it in a separate hot water cylinder. This provides a ready supply of hot water for households with greater demand. ## Combi boiler: is it right for you? [A combi boiler](https://rwmiller.com/blog/25kw-vs-30kw-combi-boiler/) is often a good choice for flats, smaller houses and homes with one bathroom. Because there is no cylinder, it takes up less space. You also get hot water whenever you need it without waiting for a storage tank to heat up. However, a combi may struggle to meet demand when several hot water outlets are being used at once. Its performance also depends on the mains water pressure and flow available at your property. ### A combi may suit you if: - You have one bathroom. - Your home has limited storage space. - You want hot water on demand. - You are replacing an existing combi boiler. - Your mains water supply has suitable pressure and flow. ## System boiler: is it a better option? A system boiler can be more suitable for a larger household with higher hot water demand. Because hot water is stored in a cylinder, several people can use showers, baths or taps around the same time without relying entirely on the boiler's instantaneous flow rate. The trade-off is that you need space for the cylinder. Installation can also be more involved if your home does not already have a suitable system. ### A system boiler may suit you if: - You have two or more bathrooms. - Several people use hot water at similar times. - You already have a hot water cylinder. - Your home has enough space for a cylinder. - You need a higher volume of stored hot water. ## How much does a new boiler cost? So, how much does a new boiler cost? There is no fixed price for every property. The final cost depends on the boiler type, output, brand and installation requirements. I currently charge £1,500–£2,800 to supply and fit a straightforward like-for-like combi boiler replacement. A more complex installation can cost more. For example, changing boiler type, moving the boiler, upgrading pipework or installing a new hot water cylinder can increase the total. When comparing quotes, look at the complete installation cost, rather than the boiler's purchase price alone. ## What boiler brands are available? The right boiler depends on your home, not just the manufacturer's name. I supply and install boilers from established manufacturers including Vaillant, Worcester Bosch and Ideal. When choosing a model, consider: - Boiler output - Energy efficiency - Warranty - Available parts and servicing - Your home's heating and hot water requirements - The installer's experience with the chosen boiler A professional assessment can help identify the appropriate size and type for your property. ## What about heat pumps? If you are replacing your heating system, you may also be considering an air source heat pump. Heat pumps work differently from gas boilers and are designed to provide heating at lower temperatures. They can be a good option for suitable properties, but installation is usually more expensive and may require [changes to your heating system](https://rwmiller.com/services/central-heating/). The suitability of a heat pump depends on factors such as insulation, heat loss, radiators, outdoor space and hot water requirements. For eligible properties in England and Wales, the Boiler Upgrade Scheme can currently provide a £7,500 grant towards an air source or ground source heat pump. ## Does installation affect the price? Yes. Two homes can need the same boiler but have very different installation costs. A simple replacement in the same location is generally less involved than changing the system or relocating the boiler. Additional work may include: - New pipework - Boiler relocation - Installing a hot water cylinder - Upgrading controls - System cleaning - Flue or condensate alterations A proper survey helps identify this work before installation begins. ## Can you finance a new boiler? Some installers offer finance options to spread the cost of a new boiler. Before agreeing to finance, check the APR, repayment period, fees and total amount repayable. A lower monthly payment does not necessarily mean a lower overall cost. If you are considering a heat pump, check whether your property qualifies for available government support. ## Which boiler should you choose? There is no single answer for every home. A combi boiler is usually worth considering when space is limited and hot water demand is relatively low. A system boiler can be a better choice when several people need hot water at the same time and there is enough room for a cylinder. A heat pump is another option if your property is suitable and you want to move towards a different type of heating system. The best choice should be based on your property's heating and hot water needs, not simply the cheapest installation price. ## Get advice on your new boiler If you are still wondering how much a new boiler costs, the most accurate answer comes from assessing your existing heating system. R.W. Miller Plumbing & Heating carries out [combi and system boiler installation](https://rwmiller.com/services/boiler-installation/) across South London and Surrey, matching the right boiler to your property and hot water demand. The team can assess your home and provide a clear quotation based on the work required. Thinking about replacing your boiler? [Contact R.W. Miller](https://rwmiller.com/contact/) to discuss your options and request a quotation. --- *Written by Reion Akim, Owner / Certified Gas Safe Engineer (Gas Safe Registration: 919881). R.W. Miller Plumbing & Heating — South London & Surrey. Call 07375 813996 for a quote.*