Choosing a new boiler for your heating system

Choosing a new boiler for your heating system2018-10-16T15:24:00+01:00
  • Heating Engineers North London
  • Vaillant Boiler Repairs and servicing
  • Vaillant boiler installers North London

When choosing a new boiler it is best to have a basic understanding of the different type of boiler that there are to choose from. Essentially there are three main types of high-efficiency gas central heating boilers – the Combination Boiler or ‘Combi’, the Conventional Boiler (Open Vent Heat Only) and the System Boiler (Sealed). Each type of boiler system delivers the benefits of the highly efficient technology inside them, but are designed to be suitable for different types of homes, plumbing and heating requirements.

A Brief Guide To The Different Types of Boilers

We will now attempt to demystify the technology within the 3 types of boilers and explain what central heating system set-ups that the boilers are best suited to.

heating-with-combination-boiler-systemCombination, or ‘combi’ boiler systems are becoming increasingly popular within the UK as they remove the need for independent tanks, pumps and valves; as these are built in within the boiler. Combination boilers heat your home and provide instant hot water as and when it is needed. The benefit of the combi boiler system is that everything is self-contained, thus reducing the space it takes up and the heating parts that may need servicing and repairs. However, combi boiler powered central heating systems do not have a hot water tank facility, so should the boiler ever breakdown, there will not be a reserve of stored hot water available. If a combination boiler system is installed in an unsuitable type of property (ie one with 2 or more bathrooms), this can lead to pressure problems when numerous systems using heated water are run simultaneously.

heating-with-open-vent-boiler-systemConventional boiler systems tend to be found in older properties. These gas central heating systems normally comprise of a heat only boiler, a copper cylinder which stores the hot water, a cold water storage tank and a Feed and Expansion tank. In a typical gas central heating system installation the mains water supply will feed into both of these tanks and the kitchen sink cold tap, and usually no more. The advantage of conventional boiler system is that they maintain a good pressure and do not suffer the pressure drops that combination boiler powered heating systems can sometimes experience. This is because the heated water is stored in a tank. One of the disadvantages of the conventional boiler and heating systems are the amount of space required to accommodate all the parts of the system; which can be quite extensive. Running costs for these systems can be relatively large and uneconomical, particularly for large properties or for only a one person household.

Central heating with a system boilerThe System boiler set up is quite similar to that of a conventional boiler, but usually the hot water cylinder is an Unvented Cylinder (for example, a Megaflow) which means that there are no cold water storage tanks or feed and expansion tanks. The hot water cylinder is mains fed so the pressure at the hot tap will be similar to the mains water cold feed entering the property. The advantages of system boiler systems are; the space savings that can be achieved by not having the tanks and the greater flow rate at the hot tap. The hot water cylinders can also be stored in garages and attics. On the flip-side, the disadvantage of a system boiler set-up can be the cost of them and the minimum requirement of a mains water flow rate of 22 litres per minute.

Important Considerations:

  • BUDGET: What can you realistically spend on a boiler and installation?

  • LOCATION: Where is the boiler to be installed and where will the flue and pipework need to run?

  • TYPE: Which type of boiler ? – Need instantaneous or stored water hot water? Save space? Greater shower pressure? An option for solar panels in the future?

  • USAGE: Consider the household size, number of people and the usage requirements. Will you need to use showers /taps at the same time?

  • FUTURE: Are you planning a loft conversion or extension? If this is the case, a system boiler with a sealed cylinder in the garage might be the best solution.

Which boiler system is right for your home and usage requirements?

Here are a few considerations you might need to think about when deciding which new boiler is most suitable for your needs.

Usage Requirement

Boiler Type

Efficiency: To improve the energy efficiency of your system Combi/Conventional/System
Instant Hot Water: You want instantaneous hot water without heating it up Combi
Extra Bathrooms: You have 2 or more bathrooms in your home Conventional/System
Limited Space: You have limited space in your flat, apartment or bungalow. Combi
Low Pressure: Your property has low water pressure Conventional
Loft Conversions: You want to carry out a loft conversion Combi/Conventional/System
Solar Power: Your wish to install solar power with a twin coil cylinder System

Choosing the right size boiler for your home

Calculating the size of your new replacement boiler is absolutely essential and ideally should be carried out by a qualified Boiler and Heating Engineer; who is experienced in properly assessing which boiler size is suited to both the property and your living requirements. The calculation is based on upon such variables as room size and orientation (btu requirements), materials, insulation and flow rate* (for Combi systems).

Choosing the best boiler size for your property is critical because of the following:

If the new boiler system is under-sized:

Here the size of the boiler (in Kilowatts) simply may not be big enough for the property and this will result in the radiators not becoming hot enough.

If the new boiler system is over-sized:

This can lead to the boiler not condensing effectively and therefore not running at its optimum efficiency. It is possible for a knowledgeable engineer to range rate the boiler during the commissioning stage of installation, However, it is better to purchase the correct boiler at the outset.

Energy Efficient Boilers

A great way to save money and reduce your carbon footprint is to buy an ‘A’ rated boiler system.

When considering a new boiler it is important to consider the energy rating because an ‘A’ rated boiler is considerably more energy efficient than an average boiler system. Quite simply, the higher the boiler rating, the less fuel the boiler consumes and CO2 produced in emissions. As a direct result of this your gas and heating costs will be significantly reduced.


  • The average boiler in the UK converts 72% of its fuel into heat; where as an ‘A’ Rated boiler will convert more than 90%!
  • If your boiler is upgraded from an ‘F’ rated boiler to an ‘A’ rated boiler you could expect to save over £100 a year extra.
  • You could reduce your household CO2 emissions by over a tonne by upgrading to an ‘A’ rated boiler.
Energy efficient boiler systems

Connecting To The Gas Supply

In order to meet gas regulations and manufacturers’ warranty requirements it is imperative that the gas supply to your boiler is sufficient. In some cases it may be necessary for your gas supply to be upgraded. As a general rule, if there is a 22mm gas supply to your boiler and the gas meter is not too far away then the supply should be good enough.

Please see our Guide to Central Heating Installations for more information.

Choosing A Boiler

There are many factors and options to consider before you choose which boiler to have installed. One of our experienced heating engineers will be able to guide you through the options that are most suitable for what you need.

You may also like to read our guides and information on:

Obtain A Full Quotation

It is always advisable to get more than one full quotation, so that you can compare and contrast the proposals, product options and prices.

It is at this point that a quote with a breakdown of what is included in the price becomes most important, because prices can vary drastically depending on the type, model and manufacturer of the boiler, additional fittings and parts (such as a Magnaclean Unit), and the incumbent labour costs for the boiler installation and any additional services such as a power flush of the heating system.

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