In this video, Steve the plumber in Clapham from demonstrates how to vent your radiators correctly.


Plumber in Clapham


Knowing how to vent your radiators correctly is a useful plumbing skill that is simple to master and can save you having to pay a call out charge for a plumber to rectify a heating problem that can be quickly and easily solved at home. However, if you live in the South West London area and do experience problems with your boiler or heating system, our team of Gas Safe heating engineers and plumbers are just a phone call or email away.

Plumbing Tips – How to Vent a Radiator

If you notice that you have no heating and or water in your heating system and the pressure is low, the first thing to do is to take a quick look your boiler (the one in the video is a Worcester Bosch boiler). If you find that the pressure gauge on the boiler is pointing to “0”. You may have to top up the pressure on your boiler. Before starting, the first thing you should do is turn your heating off.
To top the pressure up on your boiler please take a look at our “How to top up the pressure on a boiler” Video (where you will get a step by step guide on how to do this). Once the pressure on the boiler has been topped up, it is time to vent your radiators.

Things you will need:

  • A vent key.
  • An old rag.
  • A radiator (obviously!)

Once you have your vent key and old rag at the ready, find the radiator that you want to vent. Always vent your radiators starting from the bottom of the house and work your way up to the top. This is the correct way to vent a heating system; so remember – start from the bottom and move your way up.

At one end of the radiator, you will see that there is a nut (on the video this located on the left hand side of the radiator). Once you have found it, take your vent key and fit it over the nut on the radiator. Once the vent key is locked in place, turn it anti clockwise (which is the opposite way the hands on a clock travel).

Keep turning the key very slowly until you hear the hissing noise of the air inside the radiator escaping (don’t turn the key too far or you will soak the floor!). You may also see a few bubbles of water trickling out, escape too. Use the old rag to absorb the water and keep it from spilling on to your carpet or flooring.

Once most of the air has escaped through the vent (you should hear the hissing subside) and water is trickling out of the radiator with less bubbles, use the vent key to close the nut on the radiator and wipe away any excess water to save it from dripping onto your carpet or flooring. Your radiator has now been vented.

Once you have vented your radiator, you should then go back to the boiler and make sure that the pressure is back up to between 1.0 and 1.5. A classic mistake that many people can make when they vent their heating system is that they forget to fill up the system afterwards; and this can actually damage your boiler.

So always make sure that you go back to your boiler and top the pressure back up and then once the pressure is back up to 1.0, then go around and vent the other radiators in your house (if you need to do them all).

If you would like more information or would like to obtain a free quote on a heating system conversion or boiler installation, please drop an email to or call on 0208 772 8999. We have a team of friendly Gas Safe heating engineers and plumbers, local to your area and ready to help. currently covers areas in South West London, West London, Surrey and Kent. If you would like to check whether there is an plumber or heating engineer in your area, please visit our Areas Covered page for more information.