Boilers and heating systems

Replacing a boiler or carrying out alterations to heating systems requires Building Regulations consent. In practice however this is usually undertaken by specialist contractors who can self-certify their work and provide the completion certificate when the job is done.

By law, the installation of heat producing gas appliances (e.g. boilers or fires) must only be carried out by a Gas Safe registered engineer, who will be responsible for notifying Building Control. So you won’t need to make a Building Regulations application unless your contractor isn’t registered with a self-certification scheme. It’s important to be aware that if the heating engineer fails to submit notification, the owner of the property (e.g. landlord) can be subject to enforcement action.

Boilers are available that run on a wide variety of fuels, and in areas without a mains gas supply - popular alternatives include oil, bottled LPG/Calor gas and solid fuel (coal, coke, wood). Electric storage heaters are also fairly common. These take down cheaper off-peak electricity at night, store it in special bricks and release the heat the next day. They need separate electric circuits with switched fused outlets to the heaters. Although cheap to install they offer relatively little control and are one of the most expensive systems to run.

Replacement boilers

In recent years, the efficiency of boilers has made enormous progress. All new domestic boilers are now of a ‘condensing’ type designed to recycle waste heat from the hot flue gases. Most new boilers are ‘A’ rated which means they achieve efficiencies of around 90%. You can see how efficient your existing boiler is at

Depending on how they are maintained, boilers may last no more than around 15-20 years so renewal may now be overdue. Fitting a more efficient new boiler can significantly boost your home’s Energy Rating.

When it comes to selecting the right type for your home it may be worth considering installing a new combination boiler. These are very popular since they dispense with the need for separate water tanks in the loft and supply both room heating and instant hot water. Although bulkier and a little dearer than ordinary boilers they’re cheaper and simpler to install. Their limitations have traditionally been in properties with two or more bathrooms as there would only be enough hot water to serve one outlet at a time.

Modern wall-mounted boilers have small circular ‘balanced’ flues that usually project through an external wall. These are much safer than old boilers as they are ‘room sealed’, drawing air for combustion from outside (via the outer ring of the flue) and expelling exhaust gases through the same flue (inner ring). No extra air vents are therefore needed to the room in which they are situated (something that’s required for open fires). Although normally mounted on a main wall, there is some freedom about where to ‘hang’ the boiler since flues can be extended in length if they are ‘fan assisted’. Or vertical flues can be fitted that pass through a roof slope.

The rules governing location of balanced flue terminals are quite complex, but generally they should be at least 300mm away from windows, doors, eaves, gutters, airbricks etc (fan-assisted flues can be closer) and should not discharge into enclosed areas, like side passages – they must have a free flow of air passing over them.

The preferred location for boilers is within garages, kitchens or utility rooms. Locating them in bedrooms or bathrooms is normally discouraged. Boilers also need an emergency overflow pipe directed down to ground level along the outer wall surface so that should a fault develop it can safely discharge boiling water at high pressure.

Alterations to heating systems

Apart from replacing the boiler, there are some other improvements worth making to boost energy efficiency and reduce bills, or simply to make your home cosier:

Heating controls

The aim of any heating system is to provide heat where there is a demand for it and avoid wasting money and energy where there is not. A central heating system with modern programmable controls will be up to 30% cheaper to run than a standard system.

The simplest and cheapest way to set different temperatures for each room is to fit thermostatic radiator valves (TRVs) to radiators. These sense and deliver the correct amount of heat on a room by room basis and are standard for new systems. But TRVs should not be installed in the same room as any existing wall-mounted thermostat, and if a TRV is fitted to every radiator it will be necessary to fit an automatic bypass valve at the boiler (unless it already has one internally). To save energy and keep bills down TRVs can be turned off completely when rooms aren’t in use and room thermostats can be set to about 19 degrees.

You need to be able to control heating and water separately and most makes of boiler now have built-in clocks and programmers as well as a thermostat control that shuts off when the water gets to a certain temperature. A simple programmer that can set the heating to come on in the morning and again in the evening is essential to save energy, especially where a household is unoccupied during the day. More sophisticated programmable room thermostats and zoning controls allow different temperatures to be set depending on the level of occupation over a 24 hour period.

Extending the central heating

Extending a central heating system, or fitting a new one, should be within the capabilities of competent DIYers. The introduction of plastic pipes has made cutting, bending and joining pipes a lot easier. But you will still need to employ a Gas Safe registered heating engineer to install a gas boiler. For oil fired heating systems the equivalent body is OFTEC (Oil Firing Technical Association). Also, extending your existing system may require an additional electronic ‘slave’ pump to boost the flow.

Replacing existing radiators is a relatively straightforward job, particularly if the replacements are an exact match for the old ones. But before installing new radiators you need to calculate the optimum size of each radiator to heat individual rooms in terms of the required output, measured in ‘BTUs’ (British Thermal Units). If you’re employing a plumber it’s a good idea to supply them with a set of plans in advance showing exactly where you want your radiators positioned.

In timber floors pipework can be run within the floor space, taking care to minimise cutting of joists. Where floors are of concrete, pipework is best surface-run along walls and boxed in. Pipes must be well supported with plenty of clips otherwise they can be noisy and prone to damage.

Central heating systems need periodic maintenance including flushing-through to reduce limescale, and ideally should be checked annually under a service contract. Pressurised combi type systems require more frequent bleeding from time to time to release built-up air.

Boosting hot water

Traditionally, hot water is stored in an insulated copper cylinder, usually located in the airing cupboard. These generally incorporate an electric immersion heater to boost the hot water when needed. Cold water from the large storage tank in the loft refills the cylinder as hot water is drawn off at the taps. If you have this type of system in your home there are some worthwhile improvements that can be made. Lagging the cylinder with an extra insulation jacket will reduce heat loss (and bills), and fitting sophisticated ‘seven day programmer’ controls should ensure that hot water is only generated when needed. Or simply setting the hot water cylinder thermostat to about 55°C will improve energy consumption (this should be a sufficient temperature if your hot taps and shower are reasonably close to the cylinder).

However, in the last 15 years, conventional cylinders of this type have largely been superseded by mains-fed pressurised systems, such as combination boilers that heat hot water directly as it’s needed, or larger unvented hot water cylinders. So it may be worth replacing an old cylinder with a more efficient modern alternative. Pressurised hot water cylinders (such as ‘Megaflow’) do away with the need for tanks in the loft, and instead any expansion is taken by an expansion vessel. In a typical unvented system, incoming cold mains water is heated either directly in the cylinder (the ‘pressure vessel’) by means of an electric heater, or indirectly from your central heating boiler. When you open a tap, the hot water stored in the vessel is forced out by the incoming cold water, hence you get hot water at mains pressure. The downside with systems relying on mains pressure, is that the output pressure can only be as good as the quality of the supply entering the property.

Underfloor heating (UFH)

The most efficient means of delivering heat to a room is from the floor upwards. Hence underfloor heating has the advantage that it requires much lower temperatures than radiator systems to achieve the same degree of thermal comfort. This means your existing boiler could operate more efficiently, saving money and energy. UFH is claimed to offer between 15-30% greater efficiency over conventional central heating, plus there’s the added benefit of freeing up wall space with no bulky radiators.

The main type of UFH uses warm water pumped through plastic pipes laid in floor screeds over special insulation boards. This makes it less suited to retro-fitting because of the enormous amount of upheaval excavating floors etc. (although it’s often only fitted to kitchens and can be combined with an existing radiator/s). Underfloor ‘warming mats’ can be a simpler alternative for upgrading existing floors. Such ‘dry’ systems take the form of very thin flexible fabric mats containing electric heating elements which can be laid directly under floor coverings. These are ideal for background heating and taking the chill off cold stone or tile floors. Although easier to retro-fit, they are more expensive to run and best suited to smaller areas such as cloakrooms and ensuites. The downside of UFH systems is the relatively slow response time, which may not be ideal for people who only occupy the house for a few hours a day, although intelligent controls can be programmed to anticipate when warmth is required in individual rooms.