Rusty Nail

[tezestwing]

Hi About 4 years ago I had a new boiler fitted and all flushed out plus new additive put in.
I recently took a small sample of water (nice and clear not black) from my central heating radiator via the bleed screw then put a oval nail (mild steel) into this water after a week the nail went rusty,now do I really need to drain all the system water or just drain enough to add a quantity of suitable additive into the heating top up loft tank,thanks for any advice.
Regards Tez

[bhg481]

Just add the rust inhibitor. I've been adding 5 litres of Fernox 1B every 7 years since we moved into the house and no problems or need for bleeding. The Fernox instructions tell you do do exactly what you've done ie, the nail test and if it goes rusty just add inhibitor.