What a magnetic filter does
A magnetic filter (typically an Adey MagnaClean or Fernox TF1) attaches to the return pipe near the boiler and uses a powerful magnet to capture iron oxide particles before they reach the heat exchanger.
Why it matters
Iron oxide sludge is the single most common cause of premature boiler failure. It coats the heat exchanger, reducing efficiency and eventually causing it to crack — one of the most expensive boiler repairs there is.
The cost comparison
Magnetic filter fitted: £149. Heat exchanger replacement: £300–£600+. A new boiler if beyond repair: £999+. The maths is straightforward.
Manufacturer requirements
Most major manufacturers (Worcester Bosch, Vaillant, Baxi) now require a magnetic filter to be fitted for the full warranty to be valid. Without it, a sludge-related failure may be rejected under warranty.
Verdict
A magnetic filter is a non-negotiable investment on any central heating system. At £149 fitted, it's the cheapest form of boiler insurance available. We fit one on every installation as standard.