What is a good way to check if the any numerical error is occured in conjugate gradient algorithm. Additionally why is it not suggested to check error by checking A-orthogonality of search direction or checking orthogonality of residuals?

Note: here by error I mean error from floating point unit of CPU because of incorrect computation (which can be due to corrupt data in cache etc.) not due to rounding error. In some cases the errors can be due incorrect computation of matrix vector product (in cases where matrix A is not explicitly available).