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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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We had our full heating system replaced, and I can genuinely say this company acted as much more than just a supplier, they were trusted advisors throughout the entire process.

From the beginning, Ryan took the time to properly assess our situation instead of simply pushing the most expensive solution. Across three separate visits, they carefully reviewed the property, explained every option clearly, and even advised us to first contact our water provider to improve the incoming water pressure. Thanks to that advice, we were able to potentially reduce unnecessary equipment and avoid extra costs. That level of honesty and professionalism is rare.

What also stood out was how balanced their recommendations were. They guided us towards solutions that offered the best combination of quality, reliability, and cost-effectiveness rather than overselling products we didn’t need.

The installation process itself was impeccable. Everything was extremely well organised, communication was constant from start to finish, and the whole team was punctual, professional, and very respectful of our home. Every question we had was answered openly and patiently, and they were always happy to explain technical details in a way that was easy to understand.
The installation team went above and beyond, especially with the preparation and removal work. They clearly cared about doing the job properly, not just quickly, making sure the area was left in the best possible condition before setting up the new system.

A special thank you too, to Danail and Mark for their professionalism, transparency, patience, and genuine care throughout the whole project. It’s difficult to find contractors nowadays who combine technical expertise, organisation, and customer service at this level.

We would absolutely recommend them without hesitation.
Response from the owner:Thank you Rob for the terrific review. I’m really pleased our advice on the incoming water pressure and the careful, multi-visit approach helped you avoid unnecessary costs. I’ll be sure to pass your kind words on to Danail and Mark. We’re proud to be a trusted, local, community-based Surrey team and truly appreciate your recommendation. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Very happy with service from initial contact to engineer coming today. I am happy to recommend and will use company again for any future work. I have also signed up for boiler cover! Had follow up yesterday and same good service
Response from the owner:Thank you very much , Linda . We are glad that you appreciate our service and trust us by joining our service plan.
In UK from US for a month. No heat when we arrived. That did not sit well with this family from Texas. My aunt had previously used Surrey Heating for service in the past. They did not dissappoint. From initial contact, response, on-site visit, diagnosis, scheduling, and repair. All top-notch. Others in the service industry could learn a lot, in the UK and the US.
Response from the owner:Thanks Dean, so glad we could get your family’s heating sorted during your visit from Texas. We appreciate your aunt’s recommendation and are pleased our team could provide a fast response, clear diagnosis, and reliable repair. We’re a local, community-focused business and it’s great to hear we lived up to expectations. Enjoy your stay and call us anytime. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Great servive and quick respond
Response from the owner:Thanks, Tomas! We're glad you found our service helpful and that we could respond quickly. We appreciate your support. Being a trusted, local, community-based team means a lot to us. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
Super fast communication, diagnosis and repair. I will be using them in future!
Response from the owner:Thanks Rutton! I'm glad our team delivered super fast communication, diagnosis and repair. We look forward to helping you again. Thanks for trusting your local, community-based heating specialists. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
It was a routine heating service the other day. The engineer was very professional and did a thorough job checking everything over. It’s great to have the peace of mind that everything is running safely and efficiently. Great communication and arrived right on time!
Response from the owner:Thank you, Manju. I’m glad our engineer provided a professional, thorough heating service and left you with peace of mind about safety and efficiency. We pride ourselves on clear communication and punctuality as a trusted, local, community-based company. Thanks for choosing us. Ryan Price - Owner Surrey Heating Specialists Thank You, Ryan Price
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
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