In this paper an Extended Kalman Filter (EKF) and a Takagi-Sugeno observer (TSO) are presented under the impact of parameter errors as an observer for temperature monitoring, like a virtual sensor, of a embroidered metal-polymer hybrid heater structure. An implementation of the temperature estimator for health monitoring is important to guarantee a gentle, fault-free operation of the heater. It can be used to control the resulting temperature without a direct measurement or to guarantee the users' safety by reacting to overheating. Simulations justify the different observation strategies.