  We analyze quark condensates and chiral (scalar) susceptibilities including
isospin breaking effects at finite temperature $T$. These include $m_u\neq m_d$
contributions as well as electromagnetic ($e\neq 0$) corrections, both treated
in a consistent chiral lagrangian framework to leading order in SU(2) and SU(3)
Chiral Perturbation Theory, so that our predictions are model independent. The
chiral restoration temperature extracted from $<\bar q q>= <\bar u u + \bar d d
>$ is almost unaffected, while the isospin breaking order parameter $<\bar u u
- \bar d d >$ grows with $T$ for the three-flavour case SU(3). We derive a sum
rule relating the condensate ratio $<\bar q q>(e\neq 0)/<\bar q q>(e=0)$ with
the scalar susceptibility difference $\chi(T)-\chi(0)$, directly measurable on
the lattice. This sum rule is useful also for estimating condensate errors in
staggered lattice analysis. Keeping $m_u\neq m_d$ allows to obtain the
connected and disconnected contributions to the susceptibility, even in the
isospin limit, whose temperature, mass and isospin breaking dependence we
analyze in detail. The disconnected part grows linearly, diverging in the
chiral (infrared) limit as $T/M_\pi$, while the connected part shows a
quadratic behaviour, infrared regular as $T^2/M_\eta^2$ and coming from
$\pi^0\eta$ mixing terms. This smooth connected behaviour suggests that isospin
breaking correlations are weaker than critical chiral ones near the transition
temperature. We explore some consequences in connection with lattice data and
their scaling properties, for which our present analysis for physical masses,
i.e. beyond the chiral limit, provides a useful model-independent description
for low and moderate temperatures.
