HV300 can do upto 10 Rads per 1 Litre dose. You can leave this system cleaner in your system for upto 2 weeks without any detrimental effects.
When using HV300 we recommend circulating the mixture around the system for around 30 minutes to 1 hour for any average heating system or longer for heavily sludge systems.
If you do have a heavily clogged system you might want to try HV400 which is a DE-SLUDGER or HV800PF which is use for a powerflush.