As discussed at the beginning, electrical heating elements create heat via
the natural resistance of the material, and the excitation of their
molecular structure creating vibration and thus heat. This is a destructive
process, and eventually all resistive materials break down and fail.
Depending on the quality of the heating element used, this failure
could be 2 years, 5 years 10 years or 20 years; it is impossible to know
for certain as this molecular breakdown rate is dependent on a number
of factors including how many hours of use. Clearly replacing a cheap
panel heater after 2 years is more of an inconvenience than a capital
cost, but if you are employing a qualified tradesman the cost of the
installation is likely to be much more than the cost of the heater.