Unevenly heated rooms, radiators that take ages to warm up, and hot radiators next to lukewarm ones are all signs your system may need balancing, not bleeding. Understanding the difference between the two jobs is the first step to getting your heating working properly again.

Balancing vs bleeding: which job do you actually need?

Bleeding radiators removes trapped air. If the top of a radiator is cold while the bottom is hot, or you hear gurgling, bleeding is usually the answer. You release air with a bleed key until water flows steadily.

Balancing radiators is about controlling how much hot water flows through each radiator. If some radiators get roasting hot quickly while others stay cooler for a long time, the system is probably out of balance. You adjust the lockshield valves so every radiator gets its fair share of heat.

• Cold at the top and hot at the bottom: likely air, so bleeding

• All over warm, but some rooms slow to heat: likely balancing

• Cold at the bottom but hot at the top: often sludge, not bleeding or balancing alone

If your radiators have already been bled and you still have uneven heating between rooms, balancing is usually the next step.

Before you start balancing your radiators

Turn your heating off and let the system cool so you can safely handle valves and pipework. This also helps you feel temperature changes as you go without burning yourself.

Make a simple sketch of your home, marking every radiator by room and floor. This is where you will write down how many turns you make to each lockshield valve so you can return to your starting point if needed.

You will need a radiator key, an adjustable spanner or small spanner set, and a notepad or your phone notes. A digital thermometer or radiator thermometer strips can help, but are not essential for a basic home balance.

Step-by-step guide to balancing using lockshield valves

1. Fully open all radiator valves

On each radiator, open the manual side fully (this might be a wheelhead or thermostatic valve) by turning it anti-clockwise. On the opposite side, remove the plastic cap that covers the lockshield valve and open it fully as well, again turning anti-clockwise.

Note which side is the lockshield on each radiator. This is the one you will adjust to balance the system, so it is worth taking your time and clearly marking it on your room sketch.

2. Turn the heating back on and find the quickest radiator

Set your room thermostat to a high temperature so the boiler runs continuously. Wait and see which radiator heats up first. This is usually the one closest to the boiler or on the ground floor near the pipework run.

This quickest radiator is currently “hogging” the flow, so you will restrict it the most. Radiators further away will usually need their lockshields more open to get enough hot water.

3. Balance from closest to furthest, floor by floor

Start with the radiators closest to the boiler, often on the ground floor in a typical London terrace. Then work your way to the furthest radiators, usually upstairs and at the back of the house.

On each radiator:

• Close the lockshield valve fully (turn clockwise gently until it stops)

• Open it by a measured amount, for example a quarter or half turn at a time

• Write down exactly how many turns you open it on your sketch

Radiators closest to the boiler often end up nearly closed (for example a quarter to half a turn open), while the furthest radiators may need 1–2 full turns open. Allow a few minutes between adjustments for the temperature to settle.

4. Aim for even heat, not maximum heat

The goal of balancing is that all radiators warm up at a similar rate, not that each one is as hot as possible. If a nearby radiator is scorching while a far one lags behind, close the nearby lockshield a little more and open the far one slightly.

Walk the house several times as the system runs, feeling each radiator from top to bottom. Make small adjustments and update your notes, especially if you need to change things over a couple of heating cycles.

Tips for multi-floor homes, microbore and older terraces

In homes with multiple floors, begin balancing on the lowest floor and nearest radiators, then move upwards. Heat naturally rises, so you often need the upstairs lockshields slightly more open to overcome that advantage downstairs.

For microbore systems (very small 8 or 10 mm pipes), make very small lockshield adjustments, as even an eighth of a turn can make a noticeable difference. These systems can be sensitive, so keep careful notes and give extra time for temperatures to stabilise.

In older London terraces with long pipe runs and mixed-age radiators, expect some trial and error. Large old radiators near the boiler usually need their lockshields more restricted, while smaller or newer radiators at the far end often require more flow.

If one radiator is cold at the bottom…

If a radiator is hot at the top but cold at the bottom, that is usually a sign of sludge or debris collecting inside. In this case, bleeding and balancing alone will not fix the problem and you may need cleaning or flushing of that radiator or the whole system.

Balancing is still important for overall comfort, but it is only one part of keeping your heating working well. For more on sludge, symptoms and cleaning options, see our dedicated article on radiator sludge and system cleaning in the heating advice section of our site.

When to call a heating engineer

Stop and call an engineer if any lockshield or manual valve is seized, leaking, or will not turn without excessive force. Forcing stuck valves can cause damage and leaks that end up far more costly than a professional visit.

You should also seek help if you suspect sludge throughout the system, your pump seems noisy or weak, or the same radiators keep falling behind even after careful balancing. These can point to deeper issues that need proper diagnosis.

If you would like professional help with radiator balancing, full central heating checks or boiler issues, contact BeeExpress Heating & Renewables for expert Central Heating service and Boiler Repair. Call us on 02089707489 to book an engineer and get your home heating running smoothly again.