If you notice that some of your radiators get hotter than others, it 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 boiler may get hotter than those furthest away.
Because the water is pumped via a pipe, with branches to feed each radiator, the ones at the beginning of the ‘run’ tend to get more than their fair share. Remember, in most modern central heating systems, the pipe to each radiator is a branch from the main flow pipe. Near the furthest radiator, the main flow pipe turns back towards the boiler and becomes the return pipe. The pipe from each radiator then feeds back into this.
Each radiator has two valves: a control valve – the one you use to turn it on or off, and a lockshield valve – the one with a cover which you don’t normally turn.
To open or close this lockshield valve, you need to remove the cover and use a pair of pliers. It’s the lockshield valve that regulates the flow of water to each radiator. Partial closing of the lockshield valve enables you to make sure that the radiators nearest the boiler can be restricted more than those further away.
Before you can balance the system, you need radiator thermometers, which you can buy, or sometimes hire, from plumbers’ merchants. (You may have to make do with a digital thermometer.) You also need to know the order in which they heat up. To do this, turn off the heating well in advance, so that the water gets a chance to cool right down. Open both valves on all the radiators. Turn on the heating and make a note of the order in which the radiators warm up.
Turn off the heating again and let the system cool down completely. Now, turn the heating back on and go to the first radiator. You are going to adjust them in the order in which they are served. Fit the radiator thermometers to the flow and return. Turn off the lockshield valve then open it gradually again, until the difference between the two thermometers (flow to lockshield) is about 20 degrees Fahrenheit (approx. 11 degrees Centigrade).
Move on to the second radiator on the system and do the same. Repeat this procedure for all of them in order. You should find that the lockshield valve will need opening a little further on each radiator until, possibly, it is fully open on the last radiator. You should now have a perfectly balanced system where all the radiators heat up efficiently and to the same temperature.