State estimation (SE) is essential for combined heat and electric networks (CHENs) to provide a global and self-consistent solution for multi-energy flow analysis. This paper proposes an SE approach for CHEN based on steady models of electric networks (ENs) and district heating networks (DHNs). A range of coupling components are considered. The performance of the proposed estimator is evaluated using Monte Carlo simulations and case studies. Results show that a relationship between the measurements from ENs and DHNs can improve the estimation accuracy for the entire network by using the combined SE model, especially when ENs and DHNs are strongly coupled. The coupling constraints could also provide extra redundancy to detect bad data in the boundary injection measurements of both networks. An analysis of computation time shows that the proposed method is suitable for online applications