• If your radiator feels cold at the top, this can be caused by trapped air which will need to be released via the bleed screw. The steps below will help to explain the process.
  • 1. Start by turning your central heating system off. If you leave the central heating pump running this may cause more air to be drawn in to the system and you may find hot water spraying out of the radiator when it comes to bleeding it.
  • 2. Gather your tools: all you will need is a dry cloth like a tea towel, and a bowl or tray to catch water. The only specialist bit of kit you’ll need is a radiator key, which you can get cheaply at most DIY shops.
  • 3. Find the square bleed screw at the top corner of your radiator, and place the bowl or tray directly underneath it at the base of the radiator.
  • 4. Next, place the radiator key over the bleed screw (it should fit snugly), cover it with another cloth and slowly turn the key anti-clockwise for about half a turn (do not remove the bleed screw). As the air releases, youʼll hear a hissing sound. At this point, hold the cloth close to prevent water dripping or spitting.
  • 5. Once the hissing stops and water begins to trickle out steadily, tighten the screw again, being careful not to over-tighten and damage the valve.
  • 6. Switch the heating system on again.

    If your boiler has a pressure gauge, check the boiler pressure. If itʼs below the optimal level as stated in your manufacturer’s instructions, you may need to top it up by using the filling loop on your boiler. This is usually a tap or lever on the main water supply to your boiler.
  • 7. Finally, check that all the radiators are heating evenly and that none of the bleed valves are leaking. You may need to bleed some radiators a second time, but if the problem still isnʼt resolved, contact a heating engineer.
  • 8. If you have misplaced or lost your user manual, you can locate a replacement manual from this list of Vaillant boilers (please have your model number to hand).
  • We update the maintenance tips and troubleshooting guidance from time to time and aim to make it as helpful as possible. The purpose of the maintenance and troubleshooting section of this website is to provide you with general guidance. Please ensure you read and follow our instructions carefully and do not undertake the maintenance or troubleshooting unless you are aged 18 or over, are competent to do so and are confident that you can complete the maintenance. If in doubt do not attempt any actions and where an appliance is gas fuelled refer to a Gas Safe engineer for assistance.

    This website is not intended to be a substitute for professional advice and does not:
    - cover every reason that your product could fail;
    - cover all of the maintenance that can be undertaken for your product;
    - supersede any advice in your instruction manual or from your product manufacturer.

    Do not carry out any maintenance or use the troubleshooting guide if it puts you or anyone else in danger or if you believe it may cause damage to your, or another person’s property.

    If the above actions haven’t rectified your issue or you don’t feel confident to undertake them please check on-line that the terms of your plan allow for an engineer visit for this problem — https://www.domesticandgeneral.com/repairs