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combi vs system vs conventional boiler what's the difference?
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Combi vs System vs Conventional Boiler: What's the Difference?

Choosing a new boiler can be challenging, especially when trying to understand the differences between each type. You need a boiler that not only suits your home and lifestyle but is also reliable and cost-effective.

In this article, we'll guide you through the main differences between combi, system and conventional boilers. This way, you can determine which type of boiler is the ideal fit for your home.

With over a decade of expertise in boiler installation and maintenance, Surrey Heating Specialists are committed to helping you make an informed choice that aligns with your specific needs.

Combi vs system vs conventional boiler – what’s the difference?

A combination (combi) boiler is a compact unit that’s usually hung on a wall. It generates both your heating and hot water without the need for a separate hot water tank.

A conventional (also known as ‘heat-only’) boiler has a water tank. It heats your radiators up directly and connects to a separate cylinder or tank to provide hot water.

System boilers are similar to conventional boilers, but are a modern upgrade on the older model. Unlike a conventional, they don’t need both a hot and cold water tank and their pumps and valves are built-in.

Which boiler is right for me?

Combination

As they are wall hung, combination boilers are space-saving singular units, making them ideal for smaller houses. They’re also highly energy efficient – helping you to save money on bills. Plus, they’re easy to install, cheaper to maintain and easy to service, as most engineers are trained to work on combis. If you want instant hot water without having to wait for a tank to heat up, combis are best.

If you have more than one bathroom, combis can be limiting because the water pressure and flow rate will drop if people are showering at the same time, or if more than 10 radiators are in use at one time. Combis are also reliant on the water pressure from the mains – if it’s low, it’ll impact their function. There are also more moving parts, so the boiler is at increased risk of breakdown.

Conventional

Larger, older households with more than one bathroom benefit from a conventional boiler. Hot water can run from several locations at once and they don’t rely on high mains water pressure. They’re also compatible with solar heating systems and can be more cost-effective to replace.

You do have to wait for water to heat up with a conventional boiler, as water is stored in an external cylinder. Once the hot water tank runs out, you have to wait for it to refill before you have hot water. Overall, this means less efficiency and a more expensive installation cost. You also need the space to store both a hot and cold water tank/cylinder as well as the boiler itself. If this is in a cold spot like an attic, this can result in either leaks or system freeze in winter months.

System

Like a conventional boiler, a system needs an external hot water tank or cylinder – but they don’t need one for cold water. All components are integrated to take up less space, meaning a quicker install, as there are fewer pieces to fit.

As with combi boilers, system boilers rely on mains pressure, so you can face issues with flow rates or water pressure.

Find the right boiler with Surrey Heating Specialists

Looking for a new, energy-efficient boiler? Surrey Heating Specialists are here to help. With over a decade of experience, we install over 200 boilers annually, ensuring top-quality service. Enjoy the benefits of 0% interest financing, speedy installations within 48 hours, and up to 12 years of manufacturer’s warranty.

Call us now for an instant quote and experience the warmth of exceptional service! If you have further questions on which boiler type is right for you, chat with our team today. Get in touch on [email protected] or 01784-252-107.

 

 

 

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Surrey Heating Specialists replaced my old central heating boiler with a new combi boiler and removed all the old water tanks in the house. The men were very polite and the work was completed in a very professional manner and everywhere left neat and tidy afterwards. Recommend this company
Response from the owner:Thank you for the great review, we are always there to help.
Another excellent service from Surrey Heating Specalists. Signed up for the 3 star boiler cover and needed them for a leaking radiator valve. Paul came out the following day and fixed the issue with little fuss. I have been with this company for a couple of years now after having had a new boiler fitted by them and rate them 5/5. Recommend them to quite a few other people who have been more than happy with their service. Great job - thanks.
Response from the owner:Thanks Richard — really appreciate the kind words. I’m glad Paul could fix the leaking radiator valve quickly under your 3-star cover. It means a lot that you chose us for your new boiler and that you’ve been recommending our services. We’re proud to be a trusted, local, community-based business. Thanks again. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Polite, friendly and helpful in explaining what could (but hadn't) go wrong...good to know.
Will use again and did this year 2026
Response from the owner:We really appreciate you took the time to write a review, thank you!
Ryan and his team are fantastic, very professional, knowledgeable and friendly. They installed entire new heating system in my house, Ryan from the quoting side suggested the best solution ( I was thinking about heating pumps) and he promptly explained why wouldn't be the most efficient solution. From the rest of the team, same approach, before starting the job suggested the best way to run the pipes, where to locate the radiators, etc. The job couldn't be completed straight away because of my gas connections and Ryan didn't have a problem sending one of the guys after almost 2months to finalise the job. Highly recommended.
Response from the owner:Thanks Leonel, and thank you for the brilliant feedback. I’m glad our team could recommend the right heating solution, plan the pipework and radiator locations, and return to finish the install after the gas connection delay. We appreciate you trusting our local, community-based team and for recommending us. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Response from the owner:Thank you, Anne! We appreciate the 5-star rating and your support. It’s a pleasure serving our local community—please reach out if you need anything. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Great service
Response from the owner:Thank you, Calum! I’m glad you enjoyed our service. We appreciate your support of our trusted, local, community-based business. If you need anything else, please get in touch. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Dan came to fit our new boiler today and did a great job, only taking 4 hours and the job was done so well! He was really friendly and explained everything clearly. His attention to detail was clear and much appreciated! Thank you!
Response from the owner:Hi Elizabeth, thank you for the lovely feedback. I’m glad Dan fitted your new boiler quickly and explained everything clearly—his attention to detail really matters to us. We appreciate you trusting our local, community-based team. If you need anything further, please let us know. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
It was excellent service from start to finish
Response from the owner:Thanks for the great review, Fred! We’re so pleased our team provided excellent service from start to finish. As your trusted, local, community-based heating specialists, we appreciate your support. Let us know if you need anything else. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Fair pricing and great service (including the easy to book a visit, updates about the arrival time of the engineer). Would recommend and use again 👍👍
Response from the owner:Hi Speedbird1 FLY, Thank you for the great review and for highlighting our fair pricing, easy booking, and engineer arrival updates. We appreciate the recommendation. As a local, community-based business it means a lot to know we earned your trust. We look forward to helping you again. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Great service fair pricing on boiler service and repair
Response from the owner:Thanks, Jonny! Really appreciate the kind words about our boiler service and repair. Proud to be a trusted local, community-based team — here whenever you need us. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
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