If the central heating is running and most of the radiators are warm (or hot) but there’s one radiator that is warm lower down but just doesn’t seem to get heat all the way to the top then there’s probably an air-lock in it. This is the easiest thing in the world to fix and it should get that radiator working nicely again.

Equipment required:

• A radiator valve key (looks like a mini ‘T’ shaped key with a square hole in the end. Available at DIY stores if you’ve misplaced yours.
• A sheet or two of kitchen roll or other absorbent cloth

You can do this when the heating is on (or off) so let’s have a go at bleeding a radiator! It’s as simple as this:

1. Looking at the radiator that’s not warming up, at the top, there will be an end cap with a square rod in it. On some double-panel radiators, it’s hidden behind a round plastic cover that you can flick off with a fingernail.
2. Fit the radiator key over the square rod and hold the absorbent tissue around the key/valve area.
3. Unlock (counter clockwise) the valve by a half-turn or so. If it’s not been touched for ages, it might undo with a small ‘crack’ sound but this is fine. If it needs more force than you feel comfortable giving it, abandon it for now and call a pro: you might have a seized valve.
4. Whatever you do, do NOT be tempted to remove the square plug completely: undoing it a turn or two is enough for this task. All being well, you should hear a quiet hissing sound. This is the air escaping from the radiator. If the tissue immediately gets wet, tighten the valve back up (finger tight is ample): no harm done but an air lock isn’t your issue and bleeding the radiator won’t help.
5. The hissing will carry on for a while and, before too long, it’ll change to a sputtering noise or you might see a brown/blackish stain appearing on your cloth: the water has now reached the level of the valve and you can close the vent (clockwise to tighten and, again, finger tight is ample).
6. Use the cloth to dab away any dribbles that you might have missed earlier.
7. Replace any plastic covers if might have taken off.

That’s it! The radiator should now be free of air pockets which means the heated water can finally reach all the way to the top of the panel and heat the room properly. Remember to store the radiator key somewhere where you can find it next time: in the airing cupboard or somewhere near the boiler makes sense to us.

‘Bleeding’ a radiator isn’t at all harmful and won’t cause a problem if it wasn’t required in the first place so it’s always worth giving it a shot in any ‘cold radiator’ situation – but if it doesn’t help, there’s still a couple of things to check before reaching for the phone and calling your friendly plumber:

• Check the valve is open. Easy mistake to make, especially if you have thermostatic radiator valves.
• Double check the heating is actually on (i.e the radiator should be heating up). We’ve all done it!
• Check the lockshield is open. This is the valve that usually has a smooth push-on cap rather than one that has fluted sides you can grip. A small adjustable spanner is usually used to turn these valves. These should be set to balance the flow of water through the system and so they are often not set to be fully open – so if you do adjust it, remember how many turns you made so you can set it back to its old position if you need to.