You may detect that one of your radiators is warm at the top and sides but cold in the middle (take care when touching the radiator to ensure that you do not burn your hand). If this is the case you may have a build up of “sludge” in the radiator.

Most central heating systems develop this sludge over time. It starts as in the diagram below with a small amount of deposit building up in the bottom of the radiator.

radiator blockage

As the water flows past the obstruction it is diverted into a circular pattern through the radiator and this enables the build up of additional deposits over time.

radiator sludge buildup

Removing these deposits requires care. Disturbing the sludge could merely result in redistributing it throughout your other radiators, expanding the problem in future years. Worse still the sludge could reach your boiler and restrict the flow of circulating water.

You do not want to replace or update your boiler with the latest model without removing these contaminants and debris. As the sludge and general dirt are disturbed in a new installation it will find its way into your new boiler and reduce its effectiveness or life span.

The solution is for a plumber to complete a Powerflush of your system. A Powerflush will remove Magnetite sludge from your system and can also help to alleviate : –

  • Cold and inefficient Radiators
  • Boiler Deposit build up
  • Internal System Corrosion
  • Heating Pump circulation problems
  • Central Heating Pipe Blockages
  • Noisy heating systems
  • System blockages

Without a Powerflush you could see a gradual reduction in efficiency of your boiler system as this sludge coats the internal piping and reduces circulating efficiency.

In addition to reducing the issues outlined above the benefits of a professionally delivered Powerflush could be :-

  • A warmer home as the full surface of the radiator heats your room once radiator cold spots have been eradicated
  • Reduced fuel costs in future years with improved central heating system efficiency
  • Increased pump life as your central heating pump processes clear water instead of sludge
  • Reduced radiator corrosion or internal heating system corrosion.
  • Eliminating banging noises (kettling) and prolonging the boiler life

A Powerflush machine is used to complete the task. It is connected to your system and the central heating water is routed through the machine where it filters out the contaminants. The Powerflush literally flushes the new liquid through your central heating system. Once the task is completed the plumber should refill your central heating system adding a corrosion inhibitor to prolong its operating life.

Radiator sludge can lead to cold spots and some diy solutions are illustrated in this video below. Local plumbers are able to help you should this be a task too far.

19 Responses to “Radiator Sludge”

  • L.T.Bailey:

    I need a Powerflush to be done.Please advice a suitable contact in area TN16 2NB

  • Boiler Care Guide:

    Mr Bailey – we have contacted you direct with the details which should be in your email inbox by now.

  • Derek Hare:

    Would a corrosion inhibitor to be added to a system when a new boiler is installed? Would the system be flushed before such installation?

    Thanking you in anticipation.
    Derek Hare.

  • Boiler Care Guide:

    Yes, as part of many companies installation guidelines they powerflush the system fully and then add inhibitor to all new or replacement systems.

    It is starting to be a feature of many manufacturer guarantees that this type of procedure is carried out before completion of the installation.

  • Mr N Womack:

    I need a power flush on my heating system. Can you advise/recommend an approved contractor. post code CH2

  • Boiler Care Guide:

    A Powerflush is often classed as an upgrade to a Central Heating System and will therefore need a engineer to visit and provide a no obligation quotation.

  • Ady:

    Are plumbers able to power flush a one pipe radiator system. I have been informed I have sludge build up in my boiler and that a power flush will correct this? Your reply and comments/advice on this would be greatly appreciated. Thank You

  • Boiler Care Guide:

    A one pipe system can be PowerFlushed. As it is a one pipe system, it would involve the radiators being removed and taken outside to flush as the descaler does not get direct into the radiators on this particular style of system.

  • Ady:

    Has it always been a part of UK installation guidelines that they powerflush any new boiler system they fitted and then add an inhibitor to all replacement systems? If not, could you please let me know when this started. Thank You

  • Boiler Care Guide:

    It has only become common practice to flush and add inhibitor since the new condensing boiler law came in to place in April 2005.

  • Kaz Vogel:

    Can you tell me how much it would cost to have my sytem powerflushed. 2 bedrooms – 6 radiators on one level.

  • Boiler Care Guide:

    The cost of a powerflush is also influenced by access to drain points and the nature of the system so it is not possible to give an accurate quote online.

  • Assia Parveen:

    We have had our central heatingsystem for a year, it is a combi and also a condensing, but a engineer advised us to have a magnit type part fitted by the boiler, it works as a magnet collecting all deposits whilst the water is going around the system. We did have a sludge problem with a rad in the past. i wanted to know if the part that has been fitted is benificial and what is the likelyhood of sludge reappearing in to my rads?

  • Boiler Care Guide:

    Sludge does reappear in central heating systems over the years due to the different types of metals throughout the system causing electrolytic corrosion. The part that was fitted should help to collect some of the magnetic sludge that is generated.

    If the system has been flushed or is currently protected by some sort of descaler this will also help to reduce the internal chemical activity (corrosion) and slow down the generation of deposits. This is definitely beneficial to yourselves and lengthens the lifetime of your system although treating the system can never be an absolute guarantee that internal deposits will not build over the years.

  • Nick Mayes:

    I have cold spots on a few of my radiators , suspecting sludge. Can this be cured under my boiler care scheme or do I need to sort the issue separately.


  • Boiler Care Guide:

    In the first instance you should check whether bleeding the radiator cures the problem. This is a relatively easy task that any householder competent at DIY could perform themselves. There is an article within the site which outlines how to do this and the safety precautions you should take.

    Having consulted the typical terms and conditions for the boiler care plans we can advise you that: –

    When a repair is needed due to sludge (for example, damage to the pump, valves or radiators), companies will carry out this job if the parts are covered under your agreement, at no extra cost, as long as they have not already told you that you need a PowerFlush or similar procedure.

  • John Jones:

    I need a Powerflush to be done.Please advice a suitable contact in area LU7 2XG. Thank you for your help.

  • Boiler Care Guide:

    We do not have lists of Plumbers who are available to carry out a powerflush in certain postcodes although we know that companies are able to do this on a national basis, an engineer can visit to provide a no obligation quotation. The cost depends upon the ease of access to the system and radiators and the amount of time personnel will need to be at your premises.

  • Paul Davidson-P D Plumbing & Heating NR15 area:

    Do you sub contract out any power flushing work? I am a plumbing and heating engineer and would be interested in increasing the amount of power flushing that I do.