The Most Common Type of Home Central Heating

gasburnerGas is firmly established as the fuel of choice for domestic central heating systems and is responsible for around a third of the CO2 emissions produced in your home. There are different types of central hearing system (all of which MUST be fitted and maintained by a Gas Safe registered installer) and an overview is given below:

Conventional Gravity Fed System

The boiler is used to heat large amount of water which is stored in a hot water cylinder in the upstairs of the house. Hot water in this system is gravity fed and so the cylinder needs to be mounted on the top floor to ensure a useful hot water flow rate unless a pump is fitted.

The system requires two feed tanks to be installed in the loft space with one tank feeding the domestic hot water (DHW) system and the other feeding the central heating side of the system. When the hot water is exhausted it can take a long time for it to refill and this is one of the major disadvantages of this system – another being heat loss from the hot water cylinder and the fact that water is always heated whether it is required or not.


Can be fitted with a power shower or pump to provide superior flow rates and pressure.


Water must be heated and stored irrespective of demand. Requirement for loft tanks and additional pipe work.

Mains or High Pressure (HP) System

These systems use a pressure vessel to store hot water and this is forced out by the incoming mains cold water when you open the tap hence the name. These systems provide hot water at the same pressures as the cold water system and will deliver hot water much more quickly than combi boilers.

Non-vented systems have hot water stored under pressure in a pressure vessel and as a result they require annual safety inspection and certification and the ongoing cost of this should be factored in to your running costs. Vented systems use a Thermal Store to hold hot water at atmospheric pressure and so they are much safer – no annual inspection is required for these systems.

The hot water pressure performance of these systems will only meet expectations if your cold water supply can provide cold water at the required flow rate and pressure – you should have your supply tested prior to choosing this type of system as a result.

As these systems have no feed tanks, pressure levels must be checked on a regular basis in order to ensure normal operation. This is a simple operation, that requires the homeowner to check a pressure gauge and to increase the pressure as required through the use of a filling loop. A filling loop is a flexible pipe connected between the boiler and the mains cold water inlet and this is fitted with a valve that allows the user to let water in from the cold water main under pressure and this increases the pressure in the system. Despite how it may sound, this is easily performed in a few seconds and doing so requires no tools whatsoever


No requirement for loft tanks. Mains pressure hot water throughout your home. Hot water capabilities can result in almost power shower performance from a normal however, though this is totally dependant on supply pressure


More expensive to install, and also to maintain in the case of non-vented systems. Water must be heated and stored irrespective of demand.

Combi Boiler System

With a combi boiler there are no storage tanks and so your hot water is heated ‘on demand’ and this instantly makes combi boilers more efficient than those types relying on the storage of hot water for the DHW side of the system. Central Heating is called for as and when required by a programmer and in many cases (and ideally) a room thermostat. This ensures that as little energy as possible is wasted.

Combi boilers take up less space than many of their counterparts and are becoming increasingly popular – their only real drawback is that their flow rates can be quite low and this means that using more than one tap at once becomes impractical and that filling a bath can take much longer than with other systems. Combi boilers are currently unsuitable for properties with 2 or more bathrooms, although flow rates are being addressed with the newer units. It is important to ensure that you choose a boiler with a suitable rating for your property.

Condensing combi boilers offer even greater efficiency and will save you money on your fuel bills even over a standard combi. They are more expensive to purchase initially but their greatly increased efficiency means that the resulting fuel savings will pay for this.


Compact, efficient and easy to install. No requirement for tanks or storage vessels.


Low hot water flow rates.

Save Money!

There are many practical measures that you can put in place to make your home energy efficient. Some of these are extremely easy to put in place and you will soon see the savings for yourself.

  • Switch your supplier (highly recommended).

See the Gas Supply page for more information.

  • Boilers

The type and condition of your boiler is a major factor in its efficiency and therefore a modern combi boiler or condensing combi boiler will definitely save you money on your heating bills. All boilers should be inspected and serviced once a year during the summer to ensure that they will be reliable for the coming winter and beyond. It is far better that any heating problems should arise during the summer than in the middle of winter. provides a wealth of information on boiler efficiency, including a huge database of available models and their ratings.

  • Thermostatic Radiator Valves (TRVs).

These save you money by shutting of a radiator one a room has reached a preset temperature and can be installed by a plumber or a competent DIYer. With TRVs fitted, you are no longer paying for excess and unwanted heat and so there is a corresponding reduction in your heating bill.

Where TRVs are fitted to every radiator in the house it is vital that a bypass valve be fitted to the boiler. Where they are fitted to all but one radiator you should still consider the installation of a bypass valve in case someone accidentally turns off that radiator.

  • Room Thermostats

These devices are mounted on the wall of a room, normally the lounge or a commonly used living area and will save you money by switching off your boiler when the desired temperature has been reached. It is worth noting that reducing your room temperature by just one degree can result in a 10% reduction in your heating bills!

They can be divided into two types – analogue and digital. A digital room thermostat will allow you to set and view the desired and current temperatures via an LCD display whereas an analogue room thermostat will only allow you to set the desired temperature via a graduated dial.

These devices are relatively inexpensive and will quickly pay for themselves in terms of the saving on your heating bills. A room thermostats has a side effect of increasing the life of your boiler by cutting unnecessary use and these can be easily fitted by a heating engineer or a competent DIYer. Care should be taken to ensure that the chosen site is never in direct sunlight as this will distort its readings and cause it to function inaccurately.

Where wiring is a problem there is a new generation of wireless units which overcome the limitations of wired units. They are more expensive but they do allow the main thermostat unit to be placed almost anywhere in the property, while the receiver unit is wired to the boiler itself.

  • Cylinder Jackets and thermostats

Fitting a 3” thick cylinder jacket to your hot water cylinder will cut heat loss by up to 70%, increase the availability of hot water in your home and pay for itself and more in the first year. Older jackets offer less protection, so check yours now and upgrade it if necessary. Further information on central heating insulation can be found in the Central Heating Insulation section.

Fitting a cylinder thermostat means that you gain a further degree of control over your hot water – the boiler will stop heating water once the thermostat tells it that demand has been satisfied and this will result in fuel savings.

  • Draught proofing

This is a cheap and extremely effective way to ensure that the heat that you pay for stays inside your house for as long as possible. For more information please see our dedicated Draught Proofing section.

  • Double Glazing

You can cut the amount of heat lost through your windows in half by installing double glazing. Please see our dedicated Double Glazing section for further information.

  • Cavity Wall Insulation

Half of the heat in your home is lost through the walls. If you have cavity walls in your property (most properties built after ca.1930) then Cavity Wall Insulation is a must and is probably much less expensive than you might think. Please see our Cavity Wall Insulation section for further information.

  • Loft Insulation

A large proportion of the heat in your home is lost through the roof and so insulating your loft is a very effective way of cutting heat loss. Please see our Loft Insulation section for further information.