How to Balance Radiators

One radiator roasting while another barely gets warm? Your central heating may need balancing, and it’s often a manageable DIY job with a few basic tools and some patience.

Balancing your radiator controls how much hot water flows through each radiator, helping them warm your home more evenly. 

Here’s how to balance radiators step by step, including which valve to adjust and how to check you’ve got it right.

This process is for radiators and heated towel rails connected to a wet central heating system.

At a Glance

Let all the radiators cool down first: this gives you a clear starting point for checking which radiator heats up first.

• Bleed any radiators with trapped air: if a radiator is cold at the top or gurgling, bleed it before balancing the system.
• Fully open every radiator valve: turn TRVs to their highest setting and open the lockshield valves fully before testing.
• Turn the heating back on and note the order the radiators warm up: start balancing with the radiator that gets warm first, then work through the others in that order.
• Adjust the lockshield valve, not the TRV: the lockshield controls the maximum flow of hot water through the radiator and is the valve used for balancing.
• Make small lockshield adjustments: wait for the radiator temperatures to settle before checking again or making another change.
• Check the flow and return pipe temperatures: a difference of around 12°C is a commonly used target for conventional systems, unless your heating system specifies otherwise.

Our tip: Don’t assume the radiator physically closest to the boiler should be balanced first. Start with whichever radiator actually begins heating first when you switch the system on from cold.

What You’ll Need to Balance Radiators

Get everything ready before you start, as you’ll need to move between radiators while the heating cools down and warms back up.

You’ll need:

• A radiator bleed key
• An adjustable spanner or suitable lockshield valve key
• A digital thermometer
• A screwdriver if needed to remove the lockshield caps
• A cloth or towel for bleeding radiators
• Your phone or a notepad to record the order in which the radiators warm up.

How to Balance Radiators Step by Step

To balance your radiators, start with the heating system cold, find out which radiators heat first and then use each lockshield valve to adjust the amount of hot water flowing through that radiator.

Step 1 - Turn Off the Heating and Let Every Radiator Cool

Switch your central heating off and wait until every radiator is completely cold.

Starting with cold radiators lets you clearly identify which one begins warming first when you switch the heating back on.

If the system has been running for a while, give it enough time to cool properly rather than rushing to the next step.

Step 2 - Bleed Any Radiators That Need It

Bleed a radiator first if it’s cold at the top or making gurgling noises. Trapped air can stop it heating properly and interfere with the balancing process.

Bleeding and balancing do different jobs: bleeding removes trapped air, while balancing adjusts the flow of hot water between radiators.

Our guide to bleeding a radiator explains how to do this.

If you have a sealed heating system, bleeding radiators can reduce the boiler pressure. Check the pressure afterwards and follow your boiler manufacturer’s instructions if it needs topping up before continuing.

Step 3 - Fully Open the Valves on Every Radiator

Open both valves on every radiator fully before testing which ones heat first. This removes any existing restrictions that could affect the order.

If your radiator has a thermostatic radiator valve, or TRV, turn it to its highest setting.

The valve at the other end is usually the lockshield valve. It normally has a plain cap rather than a numbered temperature control. Remove the cap and turn the valve anti-clockwise until it’s fully open.

For this job, remember:

• TRV: normally controls how warm you want the room.
• Lockshield valve: controls the maximum flow through the radiator and is the valve you adjust when balancing.

Don’t assume either valve will always be on a particular side of the radiator.

Check out our guide on how thermostatic radiator valves work for more guidance on this.

Step 4 - Turn the Heating On and Record Which Radiators Warm Up First

Switch the central heating back on and check every radiator. Write down the exact order in which they begin to warm.

For example:

• Hallway
• Living room
• Kitchen
• Main bedroom
• Spare bedroom

That becomes the order you’ll use when balancing them.

Don’t simply start with whichever radiator looks closest to the boiler. The pipes may take a completely different route beneath floors and behind walls.

If you have radiators on different floors, asking somebody to help check them can make this step much easier.

Once you’ve recorded the full order, switch the heating off again and let all the radiators cool completely.

Step 5 - Start With the Radiator That Heated Up First

Begin with the first radiator on your list because it’s receiving hot water before the others and will usually need its flow restricted the most.

Close its lockshield valve fully by turning it clockwise.

Then reopen it by around a quarter of a full turn as a starting point.

Keep the TRV fully open.

Switch the heating back on and allow the radiator to warm.

Step 6 - Measure the Temperature of Both Radiator Pipes

Measure the temperature of the pipe where hot water enters the radiator and the pipe where it leaves. You’re checking the difference between these two readings.

Take the readings close to the radiator valves.

The hotter pipe is the flow pipe, carrying hot water into the radiator.

The cooler pipe is the return pipe, carrying water back into the heating system after some of its heat has been released into the room.

For example:

Around 12°C between the flow and return is commonly used as a practical target when balancing a conventional radiator system.

Your particular heating system may be designed to work with a different temperature difference, so follow the boiler manufacturer’s or heating engineer’s guidance where this specifies another target.

Step 7 - Adjust the Lockshield Valve

Make small adjustments to the lockshield until the flow and return temperatures are close to the target for your system.

If the difference between the two temperatures is too small, close the lockshield slightly to reduce the flow through that radiator.

If the difference is too large, open the lockshield slightly to allow more water through.

After every adjustment, wait for the temperatures to settle before measuring again. Turning the valve repeatedly without giving the radiator time to respond makes it much harder to judge whether your last adjustment worked.

You don’t need to chase an exact 12.0°C reading indefinitely. Aim for roughly the appropriate difference for your system.

Step 8 - Repeat With the Remaining Radiators

Move to the second radiator on your warm-up list and repeat the same process, then continue through every radiator in the order you recorded.

Radiators that warmed later will often need their lockshield valves open further because they are receiving hot water later in the circuit.

Don’t automatically open each successive valve by a set number of turns. Use the temperature readings to decide how much adjustment each radiator actually needs.

Include any heated towel rails connected to the same wet central heating circuit.

Step 9 - Check All the Radiators Again

Once you’ve balanced every radiator, let the heating system cool and run it again from cold to check the result.

The radiators should now begin warming more evenly instead of one or two getting hot while others remain noticeably cooler.

If one still heats much faster than the others, restrict its lockshield slightly. If another continues to lag behind, it may need a little more flow.

Once you’re happy with the result, return the TRVs to the settings you normally use in each room.

Leave the lockshield valves at their balanced positions.

What’s the Difference Between Bleeding and Balancing Radiators?

Bleeding removes trapped air from a radiator, while balancing controls how hot water is distributed between the radiators in your heating system.

A radiator that is cold at the top or gurgling is more likely to need bleeding.

If some radiators heat much faster than others, the system may need balancing.

You may need to do both. Bleed any affected radiators first, then balance the system.

What if Your Radiators Still Aren’t Heating Evenly?

If balancing doesn’t improve the problem, stop adjusting the lockshield valves and check for another cause.

A radiator that remains cold or heats poorly could have:

• Trapped air
• A sticking or faulty valve
• Sludge or another blockage
• A wider circulation or heating system problem.

Cold patches mainly at the bottom of a radiator can be a sign of sludge rather than poor balancing.

If several radiators remain cold, you have leaks or boiler pressure problems, or you’re unsure what is causing the issue, ask a qualified heating professional to investigate.

Balancing improves the distribution of hot water. It won’t fix every radiator fault.

Frequently Asked Questions

Can You Balance Radiators Without a Thermometer?

Yes, but using a thermometer makes balancing much more accurate.

Without one, you can still identify the radiators that heat first and gradually restrict their lockshield valves until the system warms more evenly.

A thermometer lets you compare the actual flow and return temperatures instead of relying on how hot the pipes feel by hand.

How Often Should You Balance Radiators?

You don’t need to balance radiators on a fixed schedule if they’re already heating evenly.

It’s worth checking the balance when you notice some radiators heating much faster than others or after work that changes the heating circuit, such as adding or replacing a radiator.

If everything is working properly, there’s no reason to keep changing well-balanced lockshield settings.

Get Your Radiators Heating More Evenly

Balancing your radiators comes down to a clear process: start with a cold system, record which radiators warm first, adjust their lockshield valves in that order and give every change time to settle.

Need more help with your heating? Explore our radiators, heating advice and DIY and technical advice for more practical guidance.

Know somebody who’s wearing a jumper in one room and opening the window in another? Send this guide their way.