pentair minimax nt heater wont fire

whats up pool world, My name is Rich Mihalic and I've been a poolguy for 26 years, I am looking for some support on a heater repair, coustomer has a Pentair minimax nt heater which wont fire, the digital readout reads E-- which appears to be a malfuntion of the digital readout, left side of board the Power and Pressure SW are lit and the Thermostat, Heating, and Service are not lit, I picked up a new Thermistor Probe and pluged it in and nothing changed, is the next step replaceing the board or is there something im missing or not testing.