Should you bleed upstairs or downstairs radiators first? I asked the experts for the definitive answer and why it matters

Now is the time to check your heating system so that you can ensure it is in good working order before the cold weather really sets in. And a key, very DIY-friendly part of the process is bleeding your radiators.

But when it comes to the correct order to bleed your radiators in, should you start upstairs or downstairs? I asked the experts for the definitive answer.

Should you bleed upstairs or downstairs radiators first?

You should always start by bleeding downstairs radiators first, before moving upstairs.

'It’s recommended to start bleeding your downstairs radiators first, beginning with the radiator furthest from your boiler,' explains Alex Woods from Victorian Plumbing. 'Once all of the downstairs radiators are bled, move upstairs and repeat the same process, starting with the radiator furthest from your boiler.'

But why does this order matter? 'As air naturally rises, this means any residual air in the system will be systematically moved upwards as you go through the upstairs radiators, rather than collecting in parts of the system you have already bled,' adds Alex.

To bleed your radiators, you will need:

What happens if you bleed your radiators in the wrong order?

While it's much more effective and efficient to bleed your radiators starting on the ground floor and moving upwards, the good news is that if you don't follow the advised order, you won't cause any damage to your heating system, you just might find you need to bleed your radiators again.

'Don't panic if you've started upstairs, you're not likely to damage the system doing it in the wrong order, it's just a less efficient way of getting the job done,' reveals Matthew Powell, Founder of WarmZilla. 'If you bleed the upstairs ones first then release trapped air from the downstairs radiators, air can keep moving through the system then collect back upstairs again. That can leave you needing to go back and check the upstairs radiators again, so it's just best to clear the system methodically so you don’t create extra work for yourself.

'Once you’ve finished, check the boiler pressure before switching the heating back on because bleeding radiators can reduce the pressure in a sealed system.'

Follow this step-by-step guide if you find that your boiler pressure is too low.

Should you bleed all radiators or just the one that feels cold?

It's definitely fine to just bleed a single radiator that feels cold at the top, but if you notice gurgling sounds then it might be worth taking the time to bleed each one, as Matthew explains: 'If one radiator is cold at the top and every other radiator is heating normally, you can just bleed that radiator. A cold top with a warmer bottom is a classic sign that air has collected inside it, so there’s no need to interfere with the entire system.

'If several radiators are gurgling, heating unevenly or cold across the top, I’d check each of them because that suggests trapped air is more widespread. Open each bleed valve carefully and listen for the hiss of escaping air. If water appears immediately with no air coming out, that radiator probably didn’t need bleeding.'

Once you've bled your radiators and checked your boiler pressure, turn your heating back on and check that the radiators are heating evenly. If you notice they're not, or that they are instead cold at the bottom, then it might be a sign of a problem with the valve, sludge build up in the system or your radiators may need balancing.

'If your radiator has cold spots at the bottom, the system may need flushing which is a more complicated task,' says John Klee, heating technology expert at BestHeating. 'For those who don’t feel confident in their skills it is always best to contact a qualified professional who will prevent any further problems down the line.'