The heating's on, the boiler's working, and one radiator is cold at the top and warm at the bottom. It might gurgle at you, too. Charming.

Nine times out of ten that's trapped air sitting at the top of the radiator, and getting it out is a job most people in Swindon can do themselves in about ten minutes. Here's how I'd do it.

What you'll need

  • A radiator bleed key (from any DIY shop; some newer valves take a flat screwdriver instead)
  • An old cloth or kitchen roll
  • A small bowl or cup, just in case

Before you start

  1. Turn the heating off and let the radiators cool. Hot water can spit out of the valve, and a hot radiator is no fun to lean on. Typically half an hour or so does it.
  2. Find the bleed valve. It's the small square-ended fitting at one of the top corners of the radiator.
  3. Start with the radiator furthest from the boiler if several feel cold, or simply the worst one if it's just the one.

Bleeding the radiator, step by step

  1. Hold the cloth under the valve.
  2. Fit the key and turn it slowly anticlockwise, about a quarter of a turn. Don't wind it right out.
  3. You should hear a hiss. That's the air coming out. Good.
  4. Keep the cloth there. When the hiss stops and a steady dribble of water appears, turn the key back clockwise to close it. Snug, not gorilla-tight.
  5. Wipe up any drips. The water can be dirty and will stain carpet.

Repeat on any other cold radiators.

The step everyone forgets: check the boiler pressure

Letting air out lets a little pressure out of the system too. On many combi and system boilers there's a pressure gauge on the front or underneath. Have a look once you've finished.

The right figure depends on your boiler, so check the manual, but many sit at around 1 to 1.5 bar when the system is cold. If yours has dropped well below what the manual says, it may need topping up using the filling loop, following the manufacturer's instructions.

If you're not confident doing that, or the pressure keeps dropping, stop there. Anything inside the boiler itself is a job for a Gas Safe registered engineer, and you can find one through the Gas Safe Register. I don't do gas work, full stop.

Turn the heating back on and check

Put the heating back on and give it a while. The radiator should now heat evenly, top to bottom.

When bleeding doesn't fix it

  • Cold at the bottom, warm at the top: that's often sludge, not air. Bleeding won't help.
  • Still cold all over: check the radiator valve (often a thermostatic one with numbers) isn't turned right down or stuck.
  • It needs bleeding every week: something's letting air in, or there's a leak somewhere. Get it looked at properly.
  • Water round the valves or pipes: a small weeping joint can sometimes be sorted, but keep a towel under it and don't leave it.

Want a hand?

If you'd rather someone else sorted it, or the radiator is just one job on a growing list, I work in booked 3-hour sessions in Swindon, and full-day bookings cover about 30 minutes around Swindon. I'll do my best to get the list done in the time booked. Small plumbing jobs are part of my plumbing work. Rated 4.9 on Google, insured and DBS checked.

I wrote a lighter take on this on my blog too: How to bleed a radiator, before it gurgles all winter.

Book a session or message me on WhatsApp on 07729 689420.