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22 Aug 2019

All about combi boilers

By Oliver
  • Read time: 3 minutes
A combi boiler is the most common boiler fitted in UK households. In this handy guide, put together with the help of 50five’s expert engineers, we discuss how combi’s work, explain installations and more.

How do combi boilers work?

All modern combi boilers are condensing, which means heat from flue gasses is extracted, so the amount of waste energy produced is significantly lower than on alternative boilers. So, how do they work?

One compact system heats water to supply both hot-water taps and radiators – so there is no need for a cold-water tank or hot water cylinder. Only producing water on demand, the boiler isn’t left in a constant stand-by phase.

Here are some additional benefits of combi boilers:

  • Compact in size making combi’s perfect for smaller properties

  • Ideal where there is little or no loft space

  • No risk of loft pipework freezing

  • Installation becomes quicker and cheaper as less pipework is required

  • Highly energy efficient, with a typical efficiency rating of 90% or higher

A fuel supply – gas-fired – is directed towards the burners in the boiler, which is activated via messages from valves in the system. If a valve is turned on, hot water is requested and the flowing water in the boiler is passed through a paddle switch, activating the boilers for heat. Surplus heat is stored within the heat exchanger – a small compartment within the boiler – so when the heating is on, the surplus heat is used to heat water for the taps. This is the reason why both the heating and hot water can be on at the same time.  

If central heating is required, but not hot water, the burners will heat the required pipe to provide heating in the most efficient way. Likewise, if hot water is needed but not central heating, the burners will heat the necessary pipe. Both sets of pipes run through the heat exchanger, so whether heating or hot water is required, it is all warmed through in the same way.

As all hot water is delivered at mains pressure, the need for need for separate pumps is unnecessary – so long as your mains pressure is working correctly, you will be able to enjoy a powerful shower.

boiler service

Combi boiler installation - the cost and the process

As soon as a household decides to or must consider installation a new boiler, one of the first questions asked is ‘How much will that cost?’ Many boiler installers include combi boiler prices with the overall installation price. Combi boiler prices differ, depending on various aspects such as:

  • The size of your home

  • The complexity of the boiler installation

  • The boiler type chosen e.g. manufacturer and model

  • If you require the new boiler installed in a different location than the original

Boiler installation costs differ between companies; the higher the costs, the more likely you are to receive a higher quality service. New boilers should always be installed by a Gas Safe Engineer, who will follow strict protocol to ensure your new boiler can be signed off as able and safe for use.

Combi boiler installations are made easier, as expansion vessels eliminate the need for an expansion in the roof space – which some households may not have. The waterways, heat exchanger and gas fired burner all form part of the central heating system. The flow of domestic hot water is directed to a calorifier (central heating circuit). This is made up of copper tubing, where secondary water flows as soon as the hot water tap is opened. As the water flows, heat from the primary water in the calorifier is picked up. A relief valve is installed with the piping, to ensure any built-up pressure can be released, avoiding build up which could potentially damage your system.

A pressure gauge on the combi boiler will show you the current pressure of the system – so you know whether it needs topping up, or if there is too much pressure within the system. 

To find out more about combi boiler prices, or to discuss combi boiler deals, please get in touch with our team of experts who will be more than happy to assist you in your quest for a new boiler.

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What makes a good combi boiler?

There are so many different combi boilers on the market, it can make choosing the best one for your household a difficult task. To get the best combi boiler, it is important to choose a reliable manufacturer, one that is the right size for your home – and quite importantly – have a high-quality installation carried out.

Unreliable, over and under sized boilers will mean you’re more likely to continue to spend money fixing your boiler when it breaks down.

Replacing your existing boiler can improve your homes efficiency by approx. 30% - provided you choose the right solution. Working in partnership with leading manufacturers Vaillant and Ideal Boilers, 50five provide our customers with the best possible boilers available. We are also able to offer 10 Years Parts and Labour Warranty on installations.

The boilers we install are all issued with the ‘Quiet Mark’ seal of approval – ensuring you receive minimal disruption from your boiler. Built in frost protection is also available, ensuring your system doesn’t freeze over in the colder months.

Which? Magazine have carried out a recent survey across the UK to determine the top three boiler brands across the UK – with the Vaillant EcoTec (provided by 50five), was acknowledged as third best. Pair this with our Which? Trusted Trader status, you can be sure of a quality installation and service when choosing a new combi boiler with 50five.


Written by Oliver

Oliver is a Content Specialist for 50five UK