Magnetite
In plumbing · also called Heating sludge
Black iron oxide formed as steel radiators corrode inside a heating system. It settles as sludge along the bottom of radiators and collects in pumps, valves and boilers, causing cold spots, noise and blockages. Cleaning, inhibitor and a magnetic filter keep it under control.
Using Magnetite in a plumbing system
Updated
A distinction worth remembering
Compare the cold reading with the maker's range, notice whether it falls over days or jumps when hot, and look outside for a dripping discharge pipe. Those three clues separate a leak from a vessel or valve fault.
Questions to take further
- Can I top up my boiler pressure myself?
- Many makers describe topping up a sealed system through the filling loop as a householder task. Follow the maker's instructions, top up cold, and get an engineer if it keeps dropping.
Sources
- Skills England: plumbing and domestic heating technician — The systems, materials, planning and customer responsibilities in the England occupational standard.
- HSE: domestic gas safety FAQs — Gas Safe registration and checking the categories of work on an engineer's ID card.
Where Magnetite fits in the learning path
The Central Heating section covers these topics:
- Wet Central Heating Systems
- Radiators and Heating Controls
- Heating Pressure and Safe Fault Checks
Read, practise, return
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- Heating Pressure and Safe Fault ChecksCentral Heating
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A chemical added to the water in a wet heating system to slow the corrosion of metal parts inside it. BS 7593 is the code of practice for cleaning and treating heating water. Every time fresh water goes in, for example through repeated topping up, the inhibitor is weakened.
Inhibitor
Read the Inhibitor entryCompare related terms
Open a meaning to compare its role with Magnetite, or follow its full entry.
Inhibitor
A chemical added to the water in a wet heating system to slow the corrosion of metal parts inside it. BS 7593 is the code of practice for cleaning and treating heating water. Every time fresh water goes in, for example through repeated topping up, the inhibitor is weakened.
Read the Inhibitor entryMagnetic system filter
A filter, usually fitted on the return pipe just before the boiler, with a magnet that catches magnetite as the heating water passes through. It is emptied and cleaned when the system is serviced, which also shows how much sludge the system is producing.
Read the Magnetic system filter entryBefore you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.
A definition is a start. Using it in a real question is where it sticks.