Is this in the 3NF or not?
If there is only one item of a device type from a manufacturer in inventory, then this would be 3NF.  This would be the case for the information provided.

However, it is likely that you might have more than one type of LG boiler in inventory table.  As you dig into the design more details may arise which break the 3NF conditions.    

Typically inventory items mighte have a natural key of manufacturer and manufacturer's part number.  This would be complicated if inventory items which can be sourced from different manufacturers are sold or used interchangably.  In this case, you would have an inventory (item) id for the inventory table.  This would link to a table with a tri-part key (inventory-id, manufacturer-id, manufactuers-part-number).