Magnetic filter servicing: how often it needs emptying

Practical notes on magnetic filter servicing

• The filter should be emptied at every annual service
• Heavy sludge build-up can indicate ongoing internal corrosion
• An unemptied filter offers no ongoing protection to the boiler
• Filters are usually isolated with dedicated valves for easy servicing
• Sludge colour and volume help judge whether a flush is worthwhile

Magnetic filter servicing explained in plain terms

During a service the engineer isolates the filter, drains it, and removes the magnetic core to clean off accumulated black sludge before reassembling it. The amount and colour of debris found gives a rough indication of how much corrosion is happening inside the system's radiators and pipework, and heavy sludge build-up between services can point to a system that would benefit from a full flush.

Where we deal with this

• Oakhill (BA3) · 6 mi
• Ditcheat (BA4) · 9 mi
• Priddy (BA5) · 12 mi
• Frome (BA11) · 7 mi

Questions we get asked

What happens if a magnetic filter is never emptied?

It fills up and stops capturing further debris, which means sludge starts reaching the boiler again exactly as if no filter were fitted.

Does every heating system need a magnetic filter?

It is now standard practice on new installations and strongly recommended on older systems, since it is one of the simplest ways to protect a boiler's internal components.