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Which boiler to buy: everything you need to know about boiler replacement

Real Homes logo Real Homes 10/07/2020 Sarah Warwick
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Boilers are an essential part of your home heating system but you probably won't give yours much thought – unless it breaks down! However, having the right boiler can make a huge difference to your home's efficiency and the cost of your energy bills, so it's worth learning a little bit more.

Unless you heat your home with electricity or have a heat pump, your boiler needs to work efficiently to help keep bills as low as possible. And it also requires regular maintenance to keep it working safely. So, a little bit of boiler study now will pay dividends and we promise you can get back to more exciting bits of home design after that.

This handy guide explains when it's worth replacing your boiler, the different types to consider, and how much a new boiler will cost.

Why replace your boiler?

If your boiler is more than 10 years old, it’s probably not doing the job it should be anymore. More efficient condensing boilers, which make use of the waste heat, have been mandatory since 2005. So if yours is more than a decade old, it's time to think about upgrading. 

The boiler installation experts at Heatable say replacing a very old boiler with a modern combi boiler could save you up to £400 a year on your energy bills. More standard boiler replacements will offer savings between £40 and £100 a year, which soon adds up.

If you’re planning an extension or loft conversion, the extra load that’s going to be put on your boiler – even if it is more modern – means replacement needs consideration. Your current model may not be up the job.

Which boiler should you choose?

There are three main types of boilers:

Combi boilers are the UK’s most common boiler type – they provide near instantaneous hot water on demand and require no external tanks or cylinders. 'Request hot water from your taps and the hot water is with you in seconds with a combi boiler,' says Sam Rigby, from Heatable. 

Traditionally, combi boilers are suited to small to medium size houses with two bathrooms or less. However, you can get storage combi boilers, from companies like Viessmann and Worcester Bosch, which have a built-in storage tank to provide hot water to bigger homes.

System boilers have a hot water cylinder located somewhere else in the house, which heats and stores your hot water to provide a pressurised flow. 'System boilers can be a great option for households demanding a lot of hot water at any one time, but the hot water isn’t instant and will require, potentially up to an hour (depending on boiler and cylinder size) to heat the water,' adds Sam.

Regular or ‘heat only' boilers are similar to system boilers in that they also have an external hot water cylinder, but they typically have a third component  – a cold water storage tank usually located in the loft. 'Water from the tank is gravity-fed to the below system below, usually resulting in a much lower water pressure,' says Sam. 'It’s an older way of heating a property and they’re becoming less and less common, either being pressurised and converted to system boilers or swapped entirely to combi boilers.'

As well as selecting the right type of boiler for your situation, you’ll need the right size in kW. This is determined by a heat loss calculation which takes into account the house’s size, how it’s constructed, insulation levels and airtightness, and the hot water requirements. A heating engineer should do this for you.

You don't have to stick with the same kind of boiler. It's very common to switch from a standard boiler to a combi or system.

Get a quote for a boiler replacement

You should always use a heating engineer who is a registered installer to fit a new gas boiler. Gas and LPG boilers should be fitted by someone who is Gas Safe registered. Call on an OFTEC registered installer to put in a new oil boiler. 

It’s worth getting three quotations when you’re buying a new boiler. Make sure they cover the same elements so that you’re comparing like for like. The installer will ensure the system is building regulations compliant and you should get documents to prove this. Keep these as you could be asked for them when you come to sell your home.

a man standing in front of a mirror: You can get your boiler replaced using an online provider like Heatable , which lets you change your system, move your boiler and introduce a smart thermostat (Image credit: Heatable) © Provided by Real Homes You can get your boiler replaced using an online provider like Heatable , which lets you change your system, move your boiler and introduce a smart thermostat (Image credit: Heatable)

How much does a new boiler cost?

A straightforward gas boiler replacement plus thermostatic radiator valves will typically cost about £2,300, according to the Energy Saving Trust (EST). Replacing an oil boiler will cost about £3,100.

You can also move your boiler to another room in the house. 'Additional costs to relocate a boiler during a new installation vary from nothing at all for slight moves to up to £500 for more extensive relocations to lofts spaces, different floors,' adds Sam, from Heatable.

How to take care of a boiler

For safety, boilers are designed to cut out if something is not quite right. An error code on the display will tell the engineer the cause of any problem.

A common reason for a boiler not operating is because the pressure in the system has dropped below the minimum level needed for it to work. Pressure loss is easy to resolve by topping up your system – check the boiler’s instructions to see how to do this, or ask your installer. However, it’s essential that the cause of the pressure loss is found – often this will simply be a tiny leak in the system or water supply problems in the local area.

Many problems are caused by something within the system (the pipes and radiators connected to the boiler) – usually air or dirt. Air can stop the water within the system from circulating properly, while dirt can foul parts in the boiler itself. If there are gurgling noises from radiators, or the top or bottom is cool, you’ll need to bleed the radiators. Remember to re-pressurise your system if you do this.

This may be a temporary fix, though, so your registered installer should investigate the cause. For this reason, manufacturers recommend that a central heating system is flushed before a new boiler is fitted, and that a filter is then fitted to protect the boiler from any dirt that might build up in the system over time.

An issue many combi boiler owners have experienced during harsh winters is due to frozen condensate pipes. If the pipe freezes, it will cause a boiler to shut down until the condensate melts. To prevent this, condensate pipes should be installed indoors, or adequately insulated.

A boiler should be serviced annually. This should pre-empt any problems and avoid a breakdown, as well as ensure the boiler is operating efficiently. If your boiler is still under guarantee, an annual service is usually part of the terms and conditions. It is illegal for an unqualified person to attempt to repair or install a boiler.

Tip: You may be insured for emergency boiler repairs under your home policy. However, policies may only be valid if the boiler has been serviced by a qualified person within the last 12 months, so make sure you check the details.

If you’ve taken out specialist boiler insurance you should be covered for emergency repairs and an annual service. These services generally cover repairs to the boiler, and some also cover boiler replacement, dependent on the model’s age.

What about boiler safety?

When fossil fuels, such as coal, wood, oil or gas don’t burn properly colourless, odourless carbon monoxide (CO) gas is formed, which is poisonous and can cause death. If the boiler isn’t working correctly, CO can be produced and therefore your Gas Safe or OFTEC registered engineer will check your boiler’s correct functioning and for CO during the annual service. It is also important to have an audible CO alarm in your home and to test it regularly. 

If your gas boiler has a flue that can’t be checked along its whole length, you should have inspection hatches fitted, so your installer can make sure there are no breaks in the flue that could leak carbon monoxide. If you prefer not to have hatches fitted, a boiler safety shutdown device can be installed. This features a detector that is fixed against the ceiling or wall that covers the flue, and has a sensor that goes through into the void, continuously monitoring for CO. If the poisonous gas is detected, it sends a signal to the boiler to switch off, and gives out a warning signal, so you know to call your Gas Safe-registered engineer.

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