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Heating Systems Explained

Heating Systems Explained

Gas Heating Systems

Modern gas central heating systems are safe, controllable and efficient to run but can cause confusion as they have a number of controls that you may not fully understand.

Using heating controls properly can:-

  • Improve the comfort of your home
  • Reduce the energy used and your fuel bills
  • Avoid the risk of condensation dampness
  • To get the best out of your system, you should follow the manufacturers instructions. If you have mislaid the instruction booklet for your systems, most manufacturers can provide a replacement.
Why have controls on a gas central heating system?

For a gas central heating and hot water system to operate efficiently it must be able to be controlled so that heating and hot water are provided at a suitable temperature, when and where you want it. Most systems include:-

  • Boiler (which can be a condensing, condensing combi, conventional or conventional combi model)
  • Hot water tank for systems without a combi boiler
  • Room thermostat
  • Radiators
  • Thermostatic radiator controls
  • Programmer
The Boiler

A conventional boiler heats up the water which is circulated through radiators to provide heat. The water also circulates through a coil in the hot water tank, which in turn heats up the rest of the water in the cylinder to provide running hot water.

If your boiler is a 'combi' boiler then the water is heated instantaneously when the hot water taps are switched on.

The thermostat on the boiler controls the temperature of the water circulating around the system. Please refer to the manufacturer's instructions for the optimum setting of the thermostat.

Hot Water Tank

Most hot water cylinders have a thermostat; this is recommended to be set at 60°C. To retain as much heat as possible the cylinder should have 80mm of insulation.


Radiators are most commonly used in "wet" (uses water) central heating systems. The water is heated by the boiler and travels through the radiators, giving out heat.

Thermostatic Radiator Valves (TRVs)

Thermostatic Radiator ValveTRVs are found on radiators in rooms other than where the room thermostat (see below) is placed. The TRV senses the air temperature in the room and can be set higher in the rooms you use most and lower in rooms used least such as bedrooms. They usually have a fat valve at one end, marked with a * and numbers from 1 to 5. The * setting is to protect against frost; it will typically leave the radiator switched off unless the temperature falls below about 6°C. For a normal living room, the setting of 3 or 4 is likely to be about right; for a bedroom a cooler temperature will normally be enough. Turning the dial up when the radiator is already on will not increase the room temperature! They can also be used to turn an individual radiator on or off. Generally, one radiator should be left without a TRV and left permanently switched on, this radiator may be a bathroom towel rail (where the heat is always likely to be useful), or in the same room as the room thermostat where a TRV is not needed.

Room Thermostat

ThermostatThis is usually found in the living room or hallway and is recommended to be set at 21°C. The room thermostat will respond to the temperature in the room where it is situated. When the room is warm enough it sends a signal to the central heating pump to stop heating the radiators until the temperature drops below the set level. At this point they will come back on again.

Programmer or Timer

The programmer or timer is set to control the times when the central heating and hot water are switched on and off. The average household needs heat for about 8 hours each day. But this depends on your own personal circumstances. The majority of time clocks allow you to set two 'on' and 'off' periods during the day ie 8am - 10am and 4pm - 10pm.

Heating timerSo that the house is warm when you wake up, set the heating to come on approximately 30 minutes before you get up and then in the evening set the heating to turn off about 1 hour before you go to bed. This will allow the house to warm up in the morning and cool down slightly at night.

There is a variety of programmers for operating central heating (CH) and hot water (HW). The majority have the following controls:-

  • ON/CONSTANT -HW/CH is on 24 hours each day.
  • OFF - the HW/CH is completely off.
  • ONCE - the HW/CH comes on at the first "ON" time selected and turns off at the second "OFF" time selected.
  • TWICE/AUTO - the HW/CH comes on for the 2 selected time periods.
  • HOT WATER ONLY - the heating system will not operate.

Electric Heating Systems

Electric storage heating systems are very different from a "wet" gas central heating system. The majority of homes heated by electricity have a combination of storage heaters and panel heaters with an electric immersion heater for the hot water.

Storage Heaters

Storage heaterThese operate by storing heat during 'off-peak' periods when the electricity is cheaper, usually overnight. You can only get cheap night-time electricity if you are on an off-peak tariff such as Economy 7, Economy 10 or Warmwise. This heat is then released into the room the following day and evening. There are two controls (input/charge and output/boost) on the majority of storage heaters which have to be adjusted in anticipation of the following day's weather.

Modern, slim-line storage heaters often have a charge control (or an automatic charge control) which adjusts the amount of heat stored overnight. An automatic charge control does this by measuring the temperature in the room (or more rarely, outside the house) and if it is milder, stores less heat (saving money in the process). If the storage heater has a manual charge control, you will have to make this adjustment yourself. As the weather gets colder, the input control must be set higher as the outside temperatures drop.

'Output' or 'Boost' control

Boost and output controlsThe output control tells the heater how much heat to give out during the day. If this is at the maximum setting (usually 6 or 9) you will find that the stored heat is distributed fairly quickly. It is important to set the controls to reflect the temperature outside and the times that you are in the property, eg if you are going out or to bed then turn the output down to the minimum setting.

Although storage heaters can be large and bulky in size because they use off-peak electricity they are much cheaper to run than panel heaters or bar fires. A well controlled storage heater should give you ten hours of useful heat a day. As the weather gets warmer and you find you no longer need the storage heaters on, then simply turn them off at the wall.

Be sure not to put clothing or ornaments on top of the heaters as they can become very hot and lead to a fire risk.

Electric Immersion

Most electric storage heating systems use an electric immersion to heat hot water. This may be using 'peak' or more commonly 'off-peak' electricity (usually between 11.30pm and 8.30am). If your system uses off peak to heat water then this will be controlled automatically by a timer and the whole tank will be heated for about 5 hours overnight. The water temperature can be boosted during the day, at peak rate, by overriding the timer. If using peak electricity only, switch the immersion on for the period required to heat the water. It is expensive to keep the immersion on for long periods during 'peak' times.

For Further Information Contact

Home Energy Advice Team
Kilncraigs, Greenside Street, Alloa, FK10 1EB
Tel: 01259 450000