New boiler - Inhibitor top up?

[BenH]

During an install of new boiler ('old' boiler died after 11-12 years) the system was "drained" but I guess maybe 90% of water was left in the (rather large) underfloor pipe system. What is the best way to tell how much inhibitor should be added in this case? (also taking account that system was not topped up with inhibitor for around a decade). Should I calculate amount of inhibitor needed based on amount of water drained from the central heating side or is it the total volume (CH+UFH)? Should I use a testing kit to check for amount of inhibitor?

 

[cjg]

you can test it(kit) or just put some more in another bottle should do..

 

[Lou]

What type of boiler is it?