If you find that the radiators in your home are hot in places and cold in others and in some cases just completely cold when your boiler seems to be working its socks off. The cause of this phenomenon will more than likely down to air sitting in the system. This will not cure itself and just go away, so you will need to take some action to fix this and use something called a bleed key to allow the air to escape. There are professional plumbing services like Dagenham Plumbers who can do this for you.Fitted to every radiator in a domestic central heating system there is a bleed valve on either of the top corners, it consists of a square metal block sat in the middle. The right size for a key to be placed over it.Should you not have one of these keys they can be purchased from your local plumbers merchant. Action:Isolate the boiler and pump. Fit the key and turn the block anticlockwise for one quarter of a turn. This should be enough but just in case you open it too far, have a bowl ready for any spills. Dont be tempted to open the valve further than you need to. It just results in a pool of water the floor. Listen and once the air starts to hiss from the valve, stop turning and keep the bleed key in place on the block so as soon as the air stops and water appears you will be able to shut off the radiator. A Dagenham Plumber can bleed a radiator circuit and balance the system, if you are not confident or unsure. If you get nothing is when you try to bleed the radiator, check in the loft to see if the feed and expansion tank is empty. If the tank is full, then the valve has a blockage and must be dealt with separately.