There are many different manufacturers of inhibitor, i generally either use Fernox or Sentinal, you can purchase the inhibitor either in a bottle or in what looks like a tube. Although these two types are in essence the same thing they can both be used in different ways. The one in a bottle is easier if you have an open vented system (the type with tanks in the loft) when you’re re-filling this type of system you can add the “bottle type” directly to the small tank in the loft which is then added to the system as it fills.
When you’ve got a sealed system (Combi system for example) things are a little more difficult and this is when the inhibitor in the tube comes in. There is less in the tube than there is in the bottle however it’s concentrated gel type liquid so it is the equivalent of approximately one of the bottles. This maybe easier for you to use, and make sure the heating system is still drained when you add the inhibitor. With the tube type you’ll need a silicon gun, insert the tube into the silicon gun and attach the radiator attachment which comes supplied with the inhibitor. Select a radiator (generally one upstairs is best) and, ensuring the system is still drained, you’ll need to remove the air vent pin from the top of it. Once the air vent pin is removed you’ll be able to insert the special attachment which came with the inhibitor into the tiny vent hole, with this done you can squeeze the trigger on the silicon gun thus adding the inhibitor. When the tube’s empty the job’s done, ensure you replace the vent pin and you can re-fill the system as i think i explained above. Hope this helps. Any problems call the number below.