Do your upstairs radiators get very hot, while downstairs they are just warm or even lukewarm? If so, you may need to balance your radiators.
Why do my upstairs radiators get hotter?
First off, for reasons of physics, hot water rises upwards - in much the same way as heated air in a hot air balloon moves upwards. This means that hot water will tend to stay in the upper story of a property.
This problem is often exacerbated by the fact that boilers are usually placed upstairs, which means upper-story radiators are first to receive the hot water, where it can linger.
How boilers pump water around your home
In most cases, hot water is sent from the boiler to the pump, which pushes water through the nearest radiator, then on to any other radiators on that floor. Hot water then continues to move to other radiators on different floors, by which time the water may have cooled.
If all radiators are, for example, fully open, then the upstairs radiators may receive most of the hot water, with less being distributed to lower-floor radiators.
How to balance your radiators
Balancing your radiators is fairly straightforward. You need to reduce the amount of hot water reaching the upstairs radiators, while maximising it to the lower-floor radiators. If you have two upper story radiators, for instance, first tackle the radiator nearest the boiler/pump. Close the lock-shield right down, then open it up a quarter of a turn.
For the next upstairs radiator, close the lock-shield fully, then open it up again a half turn.
Having done this, you will find the upstairs radiators take longer to get warm, but they will eventually reach the same temperature as before.
And importantly, your downstairs radiators should receive more hot water flow and heat up more quickly, reaching a more desirable temperature.
One radiator not getting warm?
Sometimes a particular radiator does not get warm - often at the extremity of a home. This will probably be remedied by balancing out your radiators.
With some lock shields you may need to remove the cap and use an adjustable spanner to turn it shut, before opening it up by the desired amount.