Flushing heating ... what to put back in?
 

This weekend, I'm draining the CH to extend a radiator and put in a few
TRV's. I've taken one rad off the wall already and the water in it was very
clear until the last bit of the water in it drained into the bucket. I'm
hoping this means my heating is generally in very good condition, as any
other house I've been in, just opening a bleed valve at the top of the
radiator would spew out vile black liquid!

Anyway, wanting to keep things this way and also to help the TRV's last as
long as possible ... what should I fill the system with after? Just water?
Worth a flush with some sort of cleaner first?




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