Treating old system before replacing a boiler

[chris911sc]

I am about to replace a Ideal Classic NF50 with a Baxi System Boiler.

Am i right to say that i should add some X400 into existing system and leave for about a week, then flush the system, replace the boiler, fill up with water and add some X100?

Thanks

 

[ChrisR]

DO you have any symptoms of corrosion - need to bleed radiator(s), some rads not so hot (esp at bottom), black water in rads, etc? X400 is very gentle and takes several weeks to do much.

Old rads? Old rad valves - any showing sign of a leak??