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Central Heating Advice


Radiators are heated by hot water from the boiler.  To ensure maximum efficiency, radiators should not have any air in them.  Cold areas at the top of the radiator, while the bottom is hot, and the heating is on is a sign that the radiator may need to be ‘bled’ to remove the air.


Bleeding a radiator

Ensure the heating is off and the radiator is cold.  By using the ‘air vent key’, the air release vent at the top of the radiator should be opened slowly until you can hear the air escaping from the radiator.  Once all of the air has been released, water will start to leak from the vent.  The air vent key should then be used to tighten the air release vent.  It is advisable to use a cloth to catch any water. 

Note: If you have a sealed system (not filled via tanks in the loft) you may need to re-pressurise the system after bleeding radiators.  If you have to bleed the radiators regularly, seek advice as this may indicate a problem.


Thermostatic radiator valves

Thermostatic radiator valves allow you to control the room temperature, they do not control the radiator temperature (this is determined by the water temperature from the boiler). 

Thermostatic radiator valves should not be covered or hidden behind furniture, as they will not be able to detect the room temperature correctly.  If there are areas on the radiator which are not as hot as others, it maybe that the thermostatic radiator valve has temporarily stopped the hot water flowing through the radiator as the room has reached temperature.

In order to maintain these valves it is advisable to manually adjust them every few months as they may become stuck.  Any damaged valves (e.g. cracked tops) should be replaced.

There should be no thermostatic radiator valve in the same room as your thermostat, this can cause a conflict of controls.


Pressure Gauge

Pressure gauges are located near to, or in, the boiler, or in the airing cupboard.  The indicator on the pressure gauge is marked in bar pressure, and should show about 1 to 1.5 bars while the heating is off. This will increase when the system is in use although should not go above 2.25 bar. 

If the pressure showing on the gauge drops, the system will require re-filling with water.  This may occur after venting the radiators or after removing and re-fitting a radiator, although can also need doing from time to time as a normal process.  If you are having to re-fill the system regularly this could indicate a leak and advice should be sought.


Time clock

Remember to adjust the time on your programmer with changing of the clocks.


Room Thermostat

Room thermostats are usually placed in either a neutral room, like a hall, or in a main living area.  This thermostat will control the heating for the whole house, therefore if the area where the thermostat is sited reaches the programmed temperature, the central heating will shut down for the whole house. 

Covering a thermostat, with curtains or furniture for example, will affect its performance, as will placing items nearby which generate heat, e.g. a lamp, television or heater.  A room thermostat should not be located on an outside wall, near a radiator or where it can receive direct sun light.

Digital thermostats display the temperature that the room is currently at, not the temperature which it has been set to.  If you over-ride the heating, remember to change it back to its original setting.  Non-digital thermostats have a dial with an arrow pointing to the temperature which the heating is set to.  You can tell the current room temperature by turning the dial slowly until you hear a faint ‘click’.  This indicates the actual room temperature, so if the dial is left at a point above the click this will mean that the heating will be on until that temperature has been reached.


Combination boilers

Combination boilers supply domestic hot water directly from the mains supply at high pressure, an advantage for things like showers which will then perform like a power shower without the need for a pump.  They are also useful if you require hot water at infrequent times, as they only heat the amount of water which is required while the tap is open.   Combination boilers do not require water tanks in the loft, nor a hot water cylinder in the airing cupboard, which create useful space.

However, a drawback with combination boilers is that you have no stored water, and will only be able to achieve a flow rate of water from the tap which the boiler is able to heat.  Also, there is no hot water stored, so in the event of a boiler breakdown or power cut you will have no hot water and no immersion heater backup system.


Hot water cylinder

Poorly insulated hot water cylinders can waste a lot of energy.  Foam encased cylinders are much better than those with red tie on jackets (which will only be on cylinders which are over 15 years old). The coil inside older cylinders will also have a smaller surface area for heating, making them less efficient.

Power Cuts

Sometimes after a power cut

Trouble Shooting

Some things to check before you call for an engineer:

Is the boiler switched on?  Make sure there have been no switches knocked or buttons pressed accidently which has turned everything off.

Does the boiler need to be reset?  Some boilers have an easily accessible reset button

Is the programmer working properly?  Do the batteries need replacing?

Does the boiler have the correct amount of pressure in it?

Is the programmer set to the correct times?

Is your room thermostat turned up

If it is an oil boiler, have you checked your oil level and pulled the pin/pressed the button to give the correct reading?



General advice

Ensure curtains don’t drape over radiators.  Most radiators work on convection, which requires cold air to flow under the radiators, then up through the convector fins and out of the top (this type of radiator will circulate warm air around the room much better than those without fins).

If possible, avoid having furniture in front of a radiator as this will also block the convection of air.

You can control the temperature of any rooms that do not need heating to the same temperature as the rest of house by adjusting the thermostatic radiator valve to a lower setting.  Always use the thermostatic valves on as lower setting as possible.

Time clocks may need to be changed with the changing of the clocks for the start and end of British Summer time.

Never block any air vents on or around the boiler, these are there for your safety.

It is recommended that your boiler is serviced annually by a qualified engineer (GAS SAFE registered for gas, OFTEC registered for oil).

Boilers should be kept clean and free from dust and dirt.  Using a clean damp cloth, it is a good idea to wipe the side panels and cabinet.

Turning a room thermostat to a higher temperature will not make the house heat up any faster.

If your heating has not come on at its specified time, it may be that the house is already at temperature.  Check the temperature on the room thermostat.

If you have a Thermal store, unvented or combination system (i.e. high pressure hot water system supplied directly from the mains such as a Powermax, Boilermate) do not leave dripping hot taps un-repaired.  This will cause the system to scale up extremely fast, and can result in having to have the appliance replaced.

If the system is drained of any water, ensure the correct amount of corrosion inhibitor is added when re-filling the system.

If you have an oil system, check your tank level regularly.  You may need to pull a pin or work a small lever on the gauge to get the correct reading. This is a safety feature to prevent the contents of the oil tank from emptying through the sight tube should it become damaged.

Please note: All of this advice is intended to assist you with understanding your central heating system.  If you are unsure of anything, we advise that you contact an appropriately qualified engineer.