We, or our supplier on our behalf, will inspect the part to work out why it failed. The guarantees cover parts that are not of acceptable quality, are not fit for a purpose you told us about, or do not match their description.
A failure is not a fault in the part where it was caused by how the part was installed, operated or maintained after supply. Common examples are dry running, cavitation, water hammer, chemical incompatibility with the pumped fluid, abrasive wear, electrical supply faults (such as voltage spikes, phase failure or missing overload protection), incorrect installation or misalignment, operation outside the manufacturer's performance curve, modification, and normal wear and tear.
A part supplied to the part number or specification you gave us is not faulty just because it does not suit your pump. Our Returns and Refund Policy explains the options in that case. Parts should be installed by suitably qualified people in line with the manufacturer's instructions.