Boilers Sheffield

Most people know, if your radiators are cold at the top and warm at the bottom they usually just need bleeding. A simple process where you turn the valve slowly and let any air out of the radiator so the water can get to the top. But what if you have a build up of magnetite in your system?

What does it mean if your radiator is hot at the top but warm at the bottom?

This could be a sign of magnetite building up in your radiators which could lead to costly problems, particularly if it reaches the inside of the boiler! Magnetite is sediment that collects in the heating system over time, which can potentially damage pipework, boiler and heating components and radiators.

Signs of Magnetite Build Up

Other signs of magnetite building up in the central heating system may be;

  • Radiators not getting as hot as they used to
  • Increased gas bills
  • Boiler making kettle sounds
  • Rust on your radiators
  • Black inky substances coming out of the radiator when they are bled


To solve this problem, there are a few solutions. Please note, all of these should be completed by a qualified professional. 

  • Firstly, a magnetic filter can be added to your central heating system. This attracts the magnetic sediment and stops it from reaching your boiler. This is vital as if the boiler components are damaged, this is likely to be the most costly to repair!
  • A central heating chemical flush can be completed. This is where chemicals are added to the central heating system to loosen any build up and are then flushed through all of the radiators and emptied out. If they are particularly bad, thick black sludge will come out!
  • A magnetic flush can be completed. This is when two extra strength magnets are attached to the central heating system to extract of the magnetic sludge built up in the system. The picture below highlights what can often be taken from central heating system when completing a magnetic flush.
Magnetite Build Up

These are just some of the options that are available, for solutions tailored to your own heating system, feel free to give us a call and we will be happy to talk through it with you. 

What to do if you think you have a build up of magnetite in your system?

Here are a few tips if you think your system may be getting clogged up with black sludge!

  • When you next book an appointment with a plumber, ask them to do a water test of your central heating water. The colour will show the water quality in the system.
  • Book an appointment with a plumber for them to give you a quote to rectify any issues you may have. If the problem is caught early it easier to solve!
  • Turn on the heating and turn off all of the radiators aside from the problem radiator. Check to see if this radiator gets hot. Slowly turn all of the other radiators back on. If the radiator stays hot, the issue was air and the problem is solved! If not, there may be a blockage in the system!


The DTS Plumbing Team

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