• The need for system cleansing comes from a build-up of oxide sludge and calcium in the central heating system. Sludge or calcium build up in a heating system means there could be an underlining problem that’s allowing air to get into the central heating system, causing radiators and heat exchangers to corrode.

    This leaves rust and debris in the bottom of radiators which corrodes down into oxide sludge. This then leads to blocked waterways in radiators, pipe work and heat exchangers.

    Blockages slow down the transfer of heat which causes pipe, valve and heating control server damage. It will, in some cases, lead to boiler replacement.

    Be warned: changing your boiler without cleansing your heating system first could lead to you needing another boiler in the near future! This also applies to the controls which may have also been replaced on the system — it can render your manufacturer's guarantee void.
  • 1. So, do you need a system cleanse? Here’s a number of symptoms to look out for:
    • Boiler switching on and off frequently (aka “cycling”)
    • Boiler constantly breaking down
    • If you have a combination boiler you may notice that the hot water keeps getting hot and then cold. A non-stable temperature may continue to get worse, until you do not get any hot water at all.
    • Boiler making banging and/or knocking noises
    • Central heating radiators taking a long time to heat up
    • Radiators getting cold spots
    • Radiators not getting very hot when the pipe work is getting hot
    • House always feels cold even when the heating’s on
    • Boiler making “kettling” noise (resembles a kettle boiling)
  • 2. What happens if I don’t cleanse my central heating system?
    • Boilers can become so damaged that they’ll be deemed uneconomical to repair, requiring a replacement
    • The efficiency of the system will be affected, costing you lots of money in fuel and system repair bills
    • Cause mechanical failure of pumps, motorised valves, heat exchangers and hydraulic systems in boilers
    • Pin holes will form in radiators and heat exchangers, requiring replacement or repair. Oxide sludge is like black muddy oil, so will damage anything it comes into contact with, such as carpets, worktops and flooring if it leaks or spills.
  • 3. What benefits can you expect after system cleansing?
    • Faster radiator “heating up” time
    • All radiators produce more heat
    • Boiler runs quieter
    • Overall central heating system quieter
    • No cold spots on radiators
    • Cheaper gas bill – making your money stretch further
    • Better hot water temperatures
    • Less risk of breakdown
    • More reliable and efficient central heating system, giving you a warmer house at less cost
  • 4. Please note: System cleansing is not covered under your Domestic and General plan or policy.
  • 5. 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.