Fan oven does not appear to function correctly.

The fan oven does not seem to achieve an acceptable operationg temperature albeit it does get hot. The red light swtches on and off when the oven is switched on indicating that the thermostat is functioning (not sure whether correctly, though). I have replaced the fan recently so am happy it is not that. I presume it must be either the element or thermostat and would welcome anyone's thoughts on this.
Thank you