How do I balance my radiators?

If some radiators are hot within minutes and others take an hour, the system isn't balanced: water takes the path of least resistance and short-circuits through the nearest radiators. Balancing evens out the flow. It takes an afternoon once and then stays done.

What you'll need

• Radiator lockshield key or small adjustable spanner
• Two thermometers, or an infrared thermometer
• Notepad

Step by step

1. Turn the heating off and let the system go completely cold.You need a cold start to observe the order radiators warm up in.
2. Open every lockshield valve fully — the plastic-capped valve, not the one you turn by hand.Count the turns as you open each one so you can return to a known point.
3. Turn the heating on and note the order in which radiators become warm.That order is your balancing order: the first to heat needs the most restriction.
4. Turn the system off, let it cool, then turn it back on and start with the first radiator to heat.You want a repeatable cold start for the measurement stage.
5. Measure the temperature of the pipe going in and the pipe coming out of that radiator.An infrared thermometer makes this straightforward. Measure on the pipe, not the valve body.
6. Close the lockshield until the difference between in and out is about 12°C, then move to the next.Close in small increments and give it a few minutes to settle before re-measuring.
7. Work through every radiator in the order they heated, finishing with the furthest.The last radiator usually ends up with its lockshield nearly or fully open.
8. Recheck the whole house after an hour and adjust anything still lagging.The system interacts — changing one radiator affects the others slightly.

Tips

• Balancing is free and often solves 'my boiler isn't powerful enough' complaints entirely.
• Do it after bleeding, not before — trapped air makes every measurement meaningless.
• Write down the final number of turns on each lockshield. If anything is disturbed later you can restore it in minutes.
• Thermostatic radiator valves control room temperature; lockshields control flow rate. They do different jobs and both matter.

Common mistakes

• Adjusting the wrong valve — The hand-operated valve or TRV is not the balancing valve. The lockshield is the one under a plastic cap.
• Balancing before bleeding — Air in a radiator makes the temperature readings meaningless.
• Closing lockshields too far — A radiator with almost no flow never heats. Small increments, and recheck.

Questions people ask