Buying Guides
Combi Boilers: Are They Right for Your Home?
Reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
A combi is the most popular boiler in the UK for good reason — but it isn’t the best fit for every home. Here’s how a combi works, where it shines, where it struggles, and what a new one costs.
Quick answer: A combi (combination) boiler heats your radiators and provides hot water on demand from a single unit — no hot-water cylinder and no tanks in the loft. That makes it compact, efficient, and cheaper to install, which is why most flats and small-to-medium homes have one. The catch is hot-water flow: a combi heats water as you use it, so running two showers at once can leave both weak. For a busy household with several bathrooms, a system boiler with a cylinder often suits better.
At a Glance
What to expect from a combi
The quick picture of how a combi behaves day to day, so you can weigh it against your home.
| Aspect | What to expect |
|---|---|
| Hot water | Heated on demand — no waiting for a tank, but one strong outlet at a time |
| Space needed | Compact; no cylinder or loft tanks, so it frees up a cupboard |
| Best suited to | Flats and small-to-medium homes with one bathroom |
| Water flow | Fine for a single shower; drops if two run together |
| Install cost | Usually the cheapest boiler type to fit |
| Running cost | Efficient — you only heat the water you actually use |
Pros & Cons
The upsides and trade-offs
The upsides
Compact and tidy with no tanks, cheaper to install, efficient because you only heat water you use, and hot water on demand with no waiting for a cylinder to reheat. Ideal for flats and smaller homes.
The trade-offs
Flow is shared — two showers at once means weak water at both. Very large homes or those with several bathrooms can outrun a combi, and mains pressure needs to be decent for a strong shower.
Engineer Insight
Who a combi really suits
For maybe eight out of ten London homes we quote, a combi is the right answer — compact, efficient and simple. The honest exception is the busy family home with two or more bathrooms in regular simultaneous use: there, a combi ends up frustrating everyone, and a system boiler with a well-sized cylinder is the better call. We size on your actual hot-water demand and mains flow rate, not just the number of bedrooms.
Costs
What a new combi costs
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Combi boilers — your questions answered
What is a combi boiler?
A combination boiler heats your radiators and your hot water on demand from one unit, with no separate hot-water cylinder or loft tanks. It’s compact, efficient, and the most common boiler type in UK homes.
Is a combi boiler right for my home?
For most flats and small-to-medium homes with one bathroom, yes — it’s compact and cost-effective. Homes with two or more bathrooms in regular simultaneous use are often better with a system boiler and a cylinder.
Can a combi boiler run two showers at once?
Not well. A combi heats water on demand and shares the flow, so running two showers together usually weakens both. If that’s a regular need, a system boiler with a stored cylinder is the better choice.
How much does a new combi boiler cost?
A like-for-like combi swap in London is typically £1,900–£3,000 supplied and fitted, depending on the model and any extra work. Converting from a system boiler costs more because of the added pipework changes.
Combi or system boiler — which is better?
Neither is ‘better’ outright — it depends on your home. Combis suit smaller homes and single-bathroom use; system boilers suit larger homes with higher, simultaneous hot-water demand. We size to your actual usage.
Related
Related guides
The alternative for bigger homes.
Read guideBuying GuidesRegular Boiler GuideFor homes with a traditional tank setup.
Read guideBuying GuidesBest Boiler BrandsWhich make to choose.
Read guideBuying GuidesNew Boiler Cost LondonWhat a replacement really costs.
Read guideCentral HeatingHow Central Heating WorksHow the boiler fits the system.
Read guideEnergy SavingBoiler Efficiency GuideGetting the most from your combi.
Read guideBrowse all Buying Guides, or head back to the Help & Advice Centre.
Combi the right choice? Let’s make sure.
Book a Gas Safe engineer to size the right boiler for your home and hot-water needs, or call for honest advice. North London, upfront pricing.
Gas Safe Registered 918817 | North London specialists | Upfront pricing