wrote in message ...
On 15 Oct,
Andy Hall wrote:

If it is a sealed system (no header tank on loft) then the only action
that should be needed with a clean system is to dose it annually with
corrosion inhibitor - cost about £20.

If it's a sealed system why dose annually? Once only should do (well
perhaps
every 10 years), unless you have a big leak.

Every 4 years.