GST ON WARRANTY AND PAID SERVICES

dear experts,
I am manufacturer, I sell goods with warranty, some are 1yr , some are 3yrs. during the warranty period i do repairs without charging any amount. even for consumables required for repairs also I am not charging anything. my question is now consumables used for repairs are chargeable to gst even I am not charging anything for it?? and i take service for repairs after warranty period also , for that I vl charge service fee as well as amount for consumables used. for this services shall o require to register for service also ?? if yes shall require to take separate registration for this?? if separate reg. required, for this threshold limit aplicable or not??