There has to be a consideration to charge GST. Since there is no consideration and spares are for free of cost. GST is not to be charged.
However you need to charge GST on warranty amount if recovered from customer.
Again you have to refer to input credit provisions, if goods are supplied for free then you will have to reverse input availed on such goods, but you need not to reverse input if warranty charges were recovered from customer, may be even a single rupee.
Your customer can avail GST input credit if you have charged GST.
chatCommentsdear sir Thanks for your immediate response. however we would like to know whether valuation have to be considered for warranty spares - Sunil Nair