The short version
- A magnetic filter traps iron oxide before it reaches the boiler
- Inhibitor must be dosed correctly and checked, not just added once
- Both are conditions of most manufacturer warranties
- Cleaning the filter is a two-minute job at the annual service
What the filter actually catches
The magnet pulls magnetite — black iron oxide sludge — out of the circulating water, and a chamber collects non-magnetic debris. That's the material that would otherwise settle in radiator bottoms and narrow heat exchanger passages.
Inhibitor is not fit-and-forget
Inhibitor gets diluted every time the system is drained or topped up, and it depletes over time. We test the concentration at service and re-dose when it's low. A system with a filter and no inhibitor is only half protected.
Where it fits in a warranty claim
When a manufacturer investigates a heat exchanger failure, system water quality is what they examine. A fitted filter, correct inhibitor level and a service history showing both were checked is the strongest position you can be in.
Common questions
Can I fit a filter to an existing system?+
Yes — it's a straightforward job on the return pipework near the boiler.
How often should the filter be cleaned?+
Annually at the service, and more often in the first year after a flush on a dirty system.
How do you test inhibitor levels?+
A test on a sample of system water during the service visit.
Do I still need a filter after a power flush?+
Especially then. The flush cleans what's there; the filter catches what forms next.
Protect the boiler you've paid for
Ask about a filter and inhibitor check at your next service.