Balancing radiators: How to balance the radiators

Balancing the radiators may be necessary if you find that some are too hot or too cold. By adjusting each radiator’s lockshield, you can control how much hot water flows through your radiators so that they all heat up evenly. Your rooms will feel more comfortable and your central heating system will be more efficient. This step-by-step guide will talk you through the process.

Why do you have to balance the radiators?

There are two main reasons. The first one is because hot water rises, and so the upstairs radiators naturally tend to get hotter than the ones downstairs. The other reason is that the water always wants to take the path of least resistance back to the pump. This is usually the shortest route in the system. In an unbalanced system, this means that the radiator closest to the pump is likely to be the hottest. If the pump is inside the boiler, the hottest radiator is probably going to be the one closest to the boiler.

Balancing central heating systems brings several advantages. Your boiler won’t need to work overtime to compensate for radiators which aren’t heating up some rooms properly. It won’t need to run for as long and may also run at a lower overall temperature, meaning cheaper fuel bills. Sometimes, in order to compensate for an unbalanced system, the pump speed may be unnecessarily increased. Balancing the system is likely to mean less wear and tear on the pump and a lower risk of water hammer.

Balancing radiators explained

This can be done in two different ways: either by feeling each radiator with your hand or with a radiator balancing kit or thermometer.

Balancing radiators without a kit

Step 1

Bleed the radiators. (If you don’t know how to do this, our how-to guide is here). Turn the central heating off and allow the system to cool down.

Step 2

Open all lockshield and thermostatic valves (TRVs) full and turn the heating on again. The lockshield is usually smaller than the TRV and has a small plastic cap on top, which must be removed. The valve cannot be operated by hand – you’ll need an adjustable spanner.

Step 3

After 20 minutes, feel each radiator. If one is distinctly hotter, close its lockshield by a quarter turn. Leave it for 20 minutes to allow the temperature to stabilise.

Step 4

Check all the radiators again. Whether another radiator or the same radiator is disproportionately hotter, close its lockshield a quarter turn. Leave it for another 20 minutes to allow the temperature to stabilise.

Step 5

Repeat the process until all radiators are the same temperature.

Balancing radiators with a thermometer or balancing kit

Step 1

Bleed the radiators. Turn the central heating off and allow the system to cool down.

Step 2

Open all lockshields and thermostatic radiator valves (TRVs). As mentioned, the lockshield is covered by a small plastic cap which must be removed. You’ll need an adjustable spanner to operate the valve itself.

Step 3

Turn your central heating back on and write down the order in which your radiators heat up. Once you’ve done that, turn your heating off again and let all the radiators cool down.

Step 4

Starting with the first radiator on your list, turn the heating back on and close the lockshield valve. Then, open it a quarter turn.

Step 5

Using a thermometer or your balancing kit, check the temperature of the pipe connected to the TRV and make a note of it. Next, check the temperature of the pipe connected to the lockshield and make a note of it. After emitting its heat, water exits the radiator via the lockshield, so this reading should be the cooler one.

You need to open the lockshield enough so that the difference between the two temperatures is 12°C. After each adjustment to the lockshield, let the temperature stabilise for 2-5 minutes before adjusting it again. This will ensure that your readings are accurate.

If your lockshield reading is higher than the TRV reading, this means that the lockshield has been fitted on the flow side of the radiator and not on the return. This is not good plumbing practice, but as long as you are adjusting the lockshield and not the TRV in order to set the 12°C discrepancy, you should be able to balance the radiator normally.

Step 6

Do the same for the rest of your radiators in the order that they heat up. Generally speaking, the further the radiator is from the boiler or pump, the more open the lockshield will need to be. You may find that on some radiators, the lockshield may need to be almost or even completely open.

Well done – you have balanced the radiators. If you have one radiator not working properly and balancing the system doesn’t make any difference, check out our page on this topic: One radiator not working: 5 common causes & how to fix.

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