• If you find a radiator isn't working properly, run through this check list to try and get it working again.

    If these tips don't help, contact us to arrange an engineer visit.
  • 1. Check the radiator valves
    Make sure the valves are all switched on.
  • 2. Check the lockshield valve
    The lockshield valve is protected by either a push on plastic cap or a plastic cap held in place by a screw. Once the protective cap has been removed you can either adjust the valve by rotating the spindle with an adjustable spanner. These valves are only adjusted when all the radiators are being balanced.
  • 3. Check the thermostat valve
    If the thermostat valve is set to 0, then the radiator won't heat up. Turn the thermostat valve to it's maximum value and wait to see if the radiator warms up.
  • 4. Check if the valves are blocked
    If the valves are correctly set open, and the radiator still isn't getting warm, the valves may be blocked with sludge made up of rust and limescale. If this is the case your heating system may need to be flushed out or run a system cleanse. Contact us for an engineer visit.
  • 5. Check if the radiators need bleeding
    If you run your hand over the surface of the radiator and only the bottom section is warm, it may mean that there is air trapped at the top preventing hot water from filling all of the radiator.

    To bleed the radiator you will need to:
    • Turn off the central heating and wait for the radiators to cool
    • Locate the bleed valve, this is found at the top of the radiator at either the right or left hand side
    • Identify the square radiator bleed screw in the centre of the bleed valve
    • Have a radiator bleed key to hand (a flat head screwdriver can be used, but the correct key is less likely to damage the bleed screw)
    • A rag to catch any drips that will be releasedLocate the bleed hole
    To bleed the radiator:
    • Place the rag under the bleed hole
    • Put the bleed key over the bleed valve screw
    • Turn the bleed key half a full turn clockwise
    • If there is air in the radiator it will escape from the bleed hole
    • When water starts to dribble from the bleed hole, turn the bleed key back one half of a full turn anti-clockwise

    If the top of the radiator is still cold when you restart the central heating system, the system may need the water supply topping up. See the Check the pressure of your system topic for more information, or contact us to arrange an engineer visit.
  • 6. Check the heating is on
    Ensure the heating system is on and the timer is set to be running when you are checking.
  • 7. Check the feed expansion tank — cold radiators upstairs
    Cold radiators located in the upstairs section of your home usually mean that the feed and expansion cistern is empty.

    • The cistern is usually found in the loft, the small tank.

    • If dry then the cistern will need to be refilled.

    • To refill the cistern simply tap the ball valve, the water should start to fill the cistern and stop when there is just enough water to float the ball valve.

    • Don't fill it up completely, as there must be enough room for the water to expand.

    Once the cistern has filled you will need to bleed the affected radiators. Check the overflow for the next couple of days to ensure the ball valve is working correctly, if it is dripping call a professional plumber to check and replace as necessary.

  • 8. Check the central heating pump — cold radiators downstairs
    If your upstairs radiators are cold and you have been through the bleeding process, then it is most likely that the central heating pump is failing. Contact us to arrange an engineer visit.
  • 9. 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.