We present a new full-discrete finite element method for the heat equation, and show the numerical stability of the method by verified computations. Since, in the error analysis, we use the constructive error estimates proposed by Nakao et al. (SIAM J Numer Anal 51(3):1525-1541, 2013) this work is considered as an extension of that paper. We emphasize that the concerned scheme seems to use the quite standard Galerkin method and is easy to implement for evolutionary equations compared with previous ones. In the constructive error estimates, we effectively use the numerical computations with guaranteed accuracy.
