If you have a mutimeter check voltage at the heater lugs. If the topside is calling for heat you should have 240v across both legs of the heater.
If its getting proper voltage but not heating, if you have access to an ampclamp(a device that measures current), check amp draw on the incoming power to the board. That is normally the easiest place to check amp draw. A typical 5.5kW heater will draw around 23-24 amps. Low speed on the pumo when heating will be around 3-4amps. If you only see the 3amps and the tub is calling for heat with proper voltage to the heater, your element is bad.
Good luck!