I have a pentair minmax nt, natural gas heater. I

I have a pentair minmax nt, natural gas heater. I am getting the E04 message. I know its a fan failure but I hear the fan fine. When I start it, and look at all the LED's in the back, all are lit up except the one labeled 'PV' under the light it says 'LED 13'. It does its three tries then the Fan LED turns off and the TFUSE and HiTemp LED stay on. Then brings up the E04. I know the TFUSE is fine because I just replaced it. What might be the problem?