Refurbishing heating system, which order should I do it?

[TheKeymeister]

I'm planning on doing some stuff to the house I've not long since moved in to, none of the radiators have TRVs so I've got a load of them and new lockshields, and also bought a Magnaclean chemical pack which came with cleaner and inhibitor. While I'm messing about fitting TRVs I intend to take the rads outside and give them a good cleaning out as well.

What should I do first? Add the cleaner and run system, drain down and fit Magnaclean and TRVs and then fill up and add inhibitor? Or should I run the cleaner through, fit the Magnaclean, let it do its thing for a bit, then drain down again and fit the TRVs, before refilling and adding inhibitor?
It's an open vented system fitted 1997 with a HRM Wallstar boiler, I've no idea if/when it was last drained down or flushed. I'm hoping to get it running a bit more efficiently ready for the winter.

 

[Doggit]

Add the cleaner and run system, drain down and fit Magnaclean unit and TRVs and then fill up and add inhibitor, but leave the TRVs fully open until you've cleaned out the Magnaclean filter.

 

[TheKeymeister]

That sounds sensible, will go for that at the weekend - cheers! Was worried about stuffing up the new TRVs with all the old **** that would get dislodged but that should sort it.