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New Boiler: What You Need to Know Before you Buy a New Boiler

How to Get the Best Boiler Installation

By Matthew Knight

Article 5 of 7

Read our guide on how to make sure you get the best boiler installation, including what to look for in your boiler installation quote.

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Buying a new boiler tends to be a decision that most people need to make in a hurry. Usually, your old boiler has broken down, it's the depths of winter and you need to get your hot water and central heating restored to its former working glory. 

Unfortunately, buying a new boiler and getting it installed can be a bit of a minefield of big decisions. Choose an unreliable boiler or make the wrong decision about part of the installation, and it's a mistake you and your bank balance will later regret. 

We've consulted industry experts so that you can know how to get the best boiler installation. This includes key decisions you need to consider that could prolong your boiler's life.

Read on to find out what you need to ask and tell your engineer when they visit to give you a quote, how to spot the telltale signs of an engineer who knows their stuff, and what you should expect from a proper boiler installation quotation.

If you want to know more about the different types of boiler, go to is a combi boiler the right boiler for you? 

Boiler installation

When you invite a heating engineer to give you a quotation for a new boiler, it should not be a quick conversation. We think a good installer should take the time to conduct a full heating survey of your home and learn all about your heating and hot water requirements before giving you their recommendation on the type and size of boiler you need. 

Here are a few questions to think about before you have a conversation with your installer:

What you need to know to get the best boiler installation

Tell your boiler installer all about your heating and hot water needs in detail, and also any future plans you might have for your home.

Have a think about the following questions and make sure you relay the answers to your heating engineer:

  • How do you use your hot water? For example, do you regularly need hot water to more than one tap or shower head at once?
  • Do you have a pumped power shower, or have plans for one in the future? Changing to a combi boiler can have many benefits, such as space-saving in the loft or airing-cupboard, but this type of boiler is not usually compatible with a shower that has a powerful electric pump. So if you do decide to get a combi boiler, you will have to ditch the pump on your shower.
  • Do your hot water requirements change throughout the year? So do say if you regularly have family or friends stay over - such as at Christmas or parties.
  • What home improvements are you planning? Your installer will need to know if you're thinking about adding an extension, loft conversion or solar panels, or if you think you might install a new bathroom or under-floor heating.
  • Are you having any problems with your system? Take the time to think about any concerns or performance issues you have with your current system, and tell your installer about them.
  • What brand of boiler do you want? The reliability of boilers varies wildly by brand, with the worst more than three times as likely to break down in the first six years compared with the best. Pick a boiler from one of the most reliable brands and be prepared to fight your corner if your engineer recommends another. Some engineers are incentivised to install boilers from particular brands, so be sure that they are recommending a brand of boiler that benefits you, rather than them.

The least reliable brand is more than three times as likely to break down, compared to the best.

The answers to these questions will be vitally important for the engineer to correctly recommend the right type and size of boiler for your home. 

What to ask the heating engineer to get the best boiler installation

When you talk to the heating engineer about your hot water needs, we think a good installer will mention some or all of the following for you to consider. If they don't come up in conversation, ask about them. 

A good installer will be able to give you a full understanding of the benefits of each extra and advise whether they are necessary. Not all these extras will be necessary for many installations. 

The cost, which will vary by property, will need to be weighed up against the benefit of having each of them done. However, extras such as a system flush and a water filter are likely to be good for the ongoing health of your boiler and prolong its lifespan.

Condensate disposal 

This is the pipework that takes water produced from the boiler away to the drain. External pipework should be kept to a minimum. If installation options only allow for external routing, the installer must ensure that the pipework is protected from freezing temperatures, in accordance with the manufacturer's instructions.

Water treatment (cleansing and flushing - around £375, based on a three-bed semi-detached house with 10 radiators) 

Most heating systems will require at least a simple gravity cleanse and flush, with the addition of a chemical inhibitor on the final fill of the system. Heavily sludged systems may require a powerflush. Your installer should advise you of which is most appropriate and why. Some basic signs of a heavily sludged system include cold spots on radiators, system noise, and excessive heat-up times. 

You can often get a rough idea of how clean or dirty the system is yourself by carefully bleeding a little water from a radiator valve, with a tissue. When refilling the heating system, ensure the installer adds a chemical inhibitor to safeguard against the formation of sludge, corrosion and scale build–up.

System filters / scale reducers (around £120, plus installation) 

Ask your installer if you need them, as they can prolong the life of a boiler. Scale reducers are particularly important for combi boilers installed in a hard-water area. It may be that a powerflush (above) or system filter is not necessary in all cases, but each of them should at least be considered by you and the installer before the installation begins. Fitting a  new boiler into a dirty or unsuitable system is a shortcut to future reliability problems.

Plume effect (water vapour from the boiler flue) 

How big a plume are you likely to get from the condensate and where is it going to be situated? Will it bother the neighbours because of where it is situated? 

It's possible to take the plume away using an additional pipe called a plume management kit.

Heating controls 

Ask if you have the required heating controls and what other options are available to you. See our guide to heating controls for more information.

Radiators 

Some older radiators may be inefficient or have internal corrosion - which means they  may need replacing. Ask your installer's advice.

Additional energy-saving measures 

New government legislation requires that each new boiler installation includes at least one of four energy-saving measures. You can choose from: flue gas heat recovery, load-compensating thermostats, weather-compensating thermostats or smart heating controls. 

Your installer should be able to talk you through the pros and cons of each and advise on the most appropriate for your home.

Checks after your boiler installation 

After installation, your installer should complete a series of safety and performance checks. The results of these should be recorded in the back of the instruction manual; this forms part of the benchmark process, which is important for the warranty. You should make sure that your installer registers your boiler with the manufacturer to activate the warranty.

If, after these checks, you notice cold spots on a radiator or it is taking too long for some radiators to heat up, this is a sign that your system hasn't been balanced or cleaned properly, so you should contact the installer immediately.

Getting the best boiler installation depends a lot on the installer you choose for the job, so pick a Which? Trusted Trader, all of whom have passed our stringent standards to become accredited. To replace a gas boiler, the installer must be Gas Safe registered - so ask to see a registration card. But we also think that you, the customer, have an important role in getting across to the installer exactly what it is you want from your new boiler. 

What should be included in a boiler installation quotation?

While quotations from heating engineers should be clear and correctly itemised, we have seen many that are bewildering.

Considering that a typical boiler installation can cost between £2,000 and £3,000, we think it is important that you know what you are paying for.

Here is what you should look for in a correctly itemised installation quote:

Essentials of an installation quote: 

  • The model, make and price of the boiler being installed. There should also be a full explanation of why that boiler has been recommended, with reference to type and size. Any extra heating controls should also be listed separately and costed.
  • The location of the boiler. An explanation of whether the boiler will remain in the same place as the previous boiler, or whether it needs to be moved. If it needs to be moved, there should be a full explanation of why.
  • Water treatment. Cleaning the system is always required, but the type of cleaning will depend on how dirty your system's water is. There are three options: gravity flush, mains flush and power flush. Your installer should be able to advise you on the most appropriate method for your heating system.
  • An overview of the works (labour costs).
  • System balancing/post-installation checks. This shouldn’t necessarily incur any extra cost, but it should be mentioned by the engineer that they will make the necessary checks that your radiators are working and correctly balanced after the installation is complete.
  • A full explanation of the warranty you are receiving with your boiler, and what needs to be done to maintain the terms of the warranty, such as an annual service.

Boiler Plus

New regulations were introduced in 2017 to govern boiler installations in England. 

  • All new gas boilers installed in England, regardless of type, need to have an ErP efficiency of at least 92%.
  • If time and temperature controls aren't already installed and working, any new boiler installation must include them.
  • If you are installing a combi boiler, one energy-saving measure, in addition to time and temperature controls (if needed), must be included.

You can choose from:

  • Flue gas heat recovery - which reuses heat from your boiler that would otherwise be wasted.
  • Load-compensating thermostat - this adjusts the radiator temperature to be hotter when your home is cold, and cooler when your home is closer to the desired temperature.
  • Weather-compensating thermostat - which is the same as a load compensating thermostat, but it adjusts the radiator temperature depending on the outside temperature.
  • Smart thermostat with automation an optimisation functions - which allow you to control your heating through a tablet or smart phone, whether you are inside our outside the home.

Speak to your engineer about which additional energy-saving device is the best for you and your budget. Some of the energy-saving devices, such as flue gas heat recovery may already be included with the boiler you have chosen. 

If you are looking for more advice on the correct type of boiler for your home, head to our guide on is a combi boiler right for you? 

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