  We derive energy-norm aposteriori error bounds, using gradient recovery (ZZ)
estimators to control the spatial error, for fully discrete schemes for the
linear heat equation. This appears to be the first completely rigorous
derivation of ZZ estimators for fully discrete schemes for evolution problems,
without any restrictive assumption on the timestep size. An essential tool for
the analysis is the elliptic reconstruction technique.
  Our theoretical results are backed with extensive numerical experimentation
aimed at (a) testing the practical sharpness and asymptotic behaviour of the
error estimator against the error, and (b) deriving an adaptive method based on
our estimators. An extra novelty provided is an implementation of a coarsening
error "preindicator", with a complete implementation guide in ALBERTA.
