• 1. The correct pressure for your boiler should be set between 1 and 1.5 bar (but always check your user manual for precise details on your system). If the pressure is below this level the boiler will not be working efficiently and could be detrimental to components in the boiler.
    Make sure you check your boiler manual for the exact pressure settings for your system.
  • 2. The boiler must be cold before adjusting the water levels. Turn the heating system OFF and wait at least an hour before you make any adjustment.
  • 3. Your boiler may have an internal or an external filling loop, which allows water to be added to the system by the opening of a tap or a valve. It is advised that the relevant page in the manual should be read before attempting to adjust the water pressure. (The following steps demonstrate an external filling loop.)
  • 4. There should be two blue taps attached to the boiler for the cold water inlet into the system. Turn both taps ON a quarter turn.
  • 5. The correct water pressure should be set between 1 and 1.5 bar (check your user manual for precise details on your system).
  • 6. Once the water pressure has reached the correct setting, turn off the water inlet taps OFF again.
  • 7. 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.