I am not a lawyer, but you have at least 2 years of warranty, and for buildings even 5. After half a year, the burden of proof reverses, but the supplier can hardly use that as an excuse. The buyer can demand from the contractor the remedy of the defect or the delivery of a defect-free item. (§439 [Baugesetzbuch])
Only if the contractor refuses both or if the repair fails twice can the buyer withdraw from the contract or reduce the price (§440/§441 [Baugesetzbuch]).
In general, a deadline for remedying the defect must be set first. The buyer has no other rights initially.
PS: Again as a note: No guarantee of accuracy, as this is all layman’s knowledge. For more details, consult a lawyer.