Some radiators sometimes get hotter than others. This can mean your central heating system is not balanced correctly. Radiators can vary in temperature because of the distance they are away from the boiler or pump and if the system is not balanced correctly the radiators nearest the source may get hotter than those furthest away.
To be absolutely sure of even temperature distribution around the home you can buy or sometimes hire radiator thermometers which clip onto the radiators pipes and measure the difference in temperature between them. The proper name for radiator thermometers is Differential Thermometers and in the digital age these have become so advanced that the temperature of both the incoming and outgoing radiator pipes can be measured, at the same time, with one thermometer. Radiator thermometers can be bought from some plumber’s merchants and have clamps, or springs attached to enable them to be clipped to the radiator valve pipes. They are not widely used in the trade and you may have to make do with a digital thermometer as shown below. Take the measurement at the flow side (wheelhead) first, then at the Lockshield and adjust accordingly using the instructions below.
To balance your central heating system, turn off the heating and allow all radiators to cool down.
Open both of the valves on all of the radiators and turn on the heating. You may need some help but you now need to go to each radiator and check the order in which they heat up. Note the order down. You will need a small spanner or an adjustable wrench to adjust the Lockshield valve.
There are two valves on all radiators. One, which is regularly used to turn the radiator on and off and one which is covered by a domed cap. The capped one is called a Lockshield valve the other is a wheelhead or control valve. You need to use grips of some kind to pull of the plastic cap from the Lockshield valve. Some Lockshield valves have a screw through the cap which must be removed before the cap can be pulled off.
Repeat the procedure above, letting everything cool down and start over again. This time as soon as you fire up the heating boiler, go to the first radiator on the system and fit the thermometers to the pipes on both valves. Turn off the Lockshield valve completely and then turn it on again slowly until the difference between the two thermometers is about 11 degrees C. Continue round the system doing the same thing. The Lockshield valve will need opening a little further on each radiator until, possibly, it is fully open on the last radiator.
To understand fully how your radiators work, go to our Central Heating - One & Two pipe systems project and our other central heating projects.
If there are radiators on the system which will not balance properly they may need to be removed and flushed out or the system may need to be drained down and cleaned. See our projects on these topics.
Why not go to our video section on balancing central heating and watch the "Central heating system" film to find out how to get the best from your central heating.