Ask the expert: Your heating questions solved

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Aimee Patterson, home heating expert at Vaillant, answers all your questions about boilers…

Q What should people consider before choosing a new heating system for their home?

A There are several factors to bear in mind, not least whether you’re looking to replace an existing system on a like-for-like basis, upgrading it to improve its performance, or planning a major project that might entail an entirely new system.

First consider whether your home is one of the 95 per cent of UK homes connected to the mains gas network. If it is, your choice of heating technology will almost always be between a boiler, a renewable technology, such as solar thermal or a heat pump, or a combination of the two (known as a hybrid system). If you’re not on mains gas, you’ll be choosing between an electric, oil or LPG system, a renewable technology, or a hybrid system.

Other factors to bear in mind are:

Your boiler supplier will be able to guide you through your choice of system and, hopefully, our advice will help you with the questions you’ll need to ask.

Q How often should a boiler be replaced?

A Most people can expect to get at least eight years’ service from their boiler, provided that it was fitted correctly and has been maintained according to the manufacturer’s recommendations. Boilers can last much longer though – we have heard of models that are more than 20 years old and still in good working order. However, boiler technology has come a long way in recent years and contemporary models are far more efficient, meaning they cost less to run. With fuel prices rising, this is a common trigger for replacing an older model. We estimate that replacing an old G-rated boiler with a high-efficiency ecoTEC (emissions control optimisation technology) model can save you around 30 per cent on gas bills * – around £300 per year.

Q How important is it to upgrade an old boiler?

A The biggest benefit is that a new model will almost certainly be more efficient and therefore cost less to run. By law, all new boilers must be high-efficiency condensing models. This means they are able to extract more energy from the fuel and turn it into useable heat. Old standard efficiency boilers can waste more than a third of the energy they produce, whereas contemporary models can be 90 per cent efficient.

An older boiler is more likely to fail without notice when winter sets in and we turn up the heating. We estimate that around three-quarters of new boilers are bought to replace an existing model and the majority are a ‘distress purchase’ to replace ones that have broken down. Boiler replacement can be quite expensive and is usually an unplanned expense, plus a breakdown can leave a homeowner without heat and hot water for several days – this can be inconvenient and uncomfortable if it occurs during the winter months. We encourage anyone with an old model to plan its replacement before a breakdown forces the decision.

Q Why do you think homeowners take their boiler for granted?

A Well, boilers aren’t that exciting! They’re often tucked away in a cupboard, or perhaps a utility room or garage, so they’re out of sight most of the time. They’re generally reliable, going about their business on a daily basis without any need for attention. So when something does go wrong, this neglect is regretted. That’s why we believe homeowners should have their boiler serviced every year. This will help ensure that it’s running as efficiently as possible, that any service requirements are spotted before they become a problem and that the terms of any guarantee are adhered to.

Q How do you spot the problems?

A The problems can manifest themselves in a number of ways. Normally, the first the homeowner is aware of them is when they realise that the heating’s not on as usual or there’s no hot water. Not all problems are serious, however. Boilers are designed with safety in mind and will cut out if they sense something is not quite right. An error code on the display will tell your installer 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 your 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.

Many problems are caused by something within the system (i.e. the pipes and radiators connected to the boiler), and usually air or dirt is to blame. Air can stop the water within the system from circulating properly, while dirt can foul parts in the boiler itself. Such problems often result in bubbling noises in your radiator(s), or the top or bottom of your radiator(s) might be cool. Bleeding the radiators will solve it (remember to re-pressurise your system if you do this), but this may be a temporary fix, so your 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. The cost of a power flush varies but is usually a few hundred pounds.

An issue many combi boiler owners experienced during the harsh winters of 2010 and 2011 was due to frozen condensate pipes. Although most installations are protected from this, those very low winter temperatures did lead to a spate of incidents. If the pipe freezes, it will cause a boiler to shut down until the condensate melts. To prevent this happing, condensate pipes should be installed indoors, or adequately insulated.

Q What maintenance can a homeowner do themselves to ensure their boiler lasts?

A There is very little you can do, apart from ensuring that it is serviced annually. Not only will a service allow any issues to be pre-empted, saving the inconvenience of a breakdown, but a correctly operating boiler will be efficient, too. 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.

Q What should people consider when looking for a boiler with good eco credentials?

A The official measure for boiler efficiency is called the SEDBUK rating. It stands for Seasonal ?Efficiency of Domestic Boilers in the UK and is the means used to compare the energy efficiency of boilers. The rating is shown as a percentage – the higher the number, the better. Currently, the most efficient boilers have a rating of around 90 per cent. So, if you’re looking to buy a boiler with good eco credentials, look for one with the highest SEDBUK rating. SEDBUK replaced the ‘A’ to ‘G’ rating type system (though some manufacturers still make reference to this). If you want to understand SEDBUK in detail, visit

Q How do you know what sort of boiler you need? Does it depend on the type of property?

A Your installer is best placed to advise you on this. The decision will be based on several factors, including property type and condition, demand (usually a calculation based on how many people live in the home) and the homeowner’s choice of heat emitter (such as radiators or underfloor heating).

Most homes in the UK (around 95 per cent) are connected to the gas mains. There are three main types of gas boiler system:

In existing properties, it’s quite common to choose a like-for-like replacement – for example, upgrading an old system model for a new one – but some older open-vent systems may benefit from an upgrade to a system or combi boiler. Again, your installer is best placed to advise you.

Combi (or combination) boilers heat water on demand rather than heating and then storing a large volume of hot water in a separate cylinder. This is efficient and makes it ideal for properties with limited space, as the separate cylinder is not needed. Combi boilers are best suited to homes with a single bathroom; homes that need larger supplies of hot water (for example, those with several bathrooms) are usually suited to a system boiler or open-vent boiler with an adequately sized cylinder.

If you’re replacing the heating system as a part of an extension or refurbishment, or embarking on a self-build project, you should also think about using a renewable technology, such as solar thermal or a heat pump, to meet some or all of your heating and hot water needs.

Q Why did Vaillant produce the Jargon Buster?

A We produced the plain English guide to help homeowners understand the problems that can arise and to give advice on buying a new boiler. We spoke to 1,000 homeowners, and three in five said a guide would be useful when dealing with plumbers. Just over a third were not very confident about handling tradespeople, while a quarter of those who had a boiler breakdown said they didn’t really understand what they were told. Another third didn’t feel in control or able to influence the decision to repair or replace. Almost all (95 per cent) expressed an interest in understanding what work was being done and three-quarters said they turned to the internet to find answers.

Our guide was awarded the ‘Crystal Mark’ by the Plain English Campaign, which praised Vaillant for the initiative, and it is free to download from or can be ordered by emailing or calling 01773 596013.

Q How do people find a reliable boiler fitter/maintenance person?

A There is a searchable directory of Vaillant Advance installers at These are independent installers who have been trained at one of our Centres of Excellence. We recommend that you get a quotation from three installers before appointing one to do the work. All domestic boiler installers in the UK must be registered with a competent person’s scheme such as Gas Safe; that way you know that your boiler will be installed correctly. It’s worth asking neighbours and friends if they can recommend a local installer. Many have a client base built on word-of-mouth recommendations, so they don’t advertise themselves at all.

Q What new eco technologies are available for heating the home?

A While the boiler remains the number one means, and is likely to remain so for many years due to its comparatively low cost and the almost ubiquitous supply of mains gas, a number of options now exist for homeowners looking for a ‘greener’ choice.

Renewable technologies, which harness natural resources to provide heating, electricity and hot water for your home, include solar thermal, air-source heat pumps and ground-source heat pumps.

There are ways of making your gas boiler more efficient. The gas that leaves the boiler via the flue contains latent (hidden) heat that can be recovered and used. A passive flue gas recovery device (called PFGHRD) can be used with various gas-fired combination boilers to extract heat from these gases. This recovered heat is then used to pre-heat cold water before it enters the boiler to be heated for domestic hot water. The device is installed above the boiler, allowing the flue gases to pass through the device after leaving the boiler.

Solar thermal heating systems use the sun’s free, renewable energy to heat hot water. These systems generate hot water using radiation from the sun through a collector, which is usually on the property’s roof. These collect heat from the sun and use it to heat up water that is stored in a hot water cylinder. When solar energy is unavailable or when the water needs to be hotter, a conventional boiler or immersion heater may be used. Collectors may be flat plate or evacuated tube panels – flat plates are usually preferred for domestic use due to their appearance.

Heat pumps are devices that turn low temperature heat into higher temperature heat. An air-source heat pump (ASHP) takes in heat energy from the outside air in the same way that a fridge expels heat from its interior. This energy can then be used to heat radiators, underfloor heating systems and hot water.

A ground-source heat pump (GSHP) works in a similar way to an air source heat pump, but instead of taking in heat from the air, it uses a loop of pipes that are buried in the garden, or bore holes, to capture heat energy from the ground. This energy can then be used to heat radiators, underfloor heating systems and hot water.

There are also systems that can help with the circulation of fresh air within the home. These are particularly useful in thermally efficient homes as it means windows can remain closed and a balanced temperature be maintained. A mechanical ventilation heat recovery (MVHR) system removes the warm, moist air and contaminants from rooms such as kitchens and bathrooms. The air is then passed through a heat exchanger and expelled outside. Fresh air from outside is then drawn in and passed through the heat exchanger, which warms the air. The fresh, warmed air is then supplied to living rooms and bedrooms via ducts.

Under the recently introduced Renewable Heat Incentive (RHI) scheme, it is possible to receive ‘cashback’ from the Government for these and other renewable technologies. The scheme has been introduced to encourage the uptake of such systems and to soften the upfront cost. Depending on your property and the system installed, RHI and the accompanying fuel savings mean that the system can pay for itself in as little as four years. For more information on renewable technologies and their suitability for your home, we recommend a browse around the Energy Savings Trust’s website –