I have a MiniMax NT Heater and when turning it on, EO 5 message

Any fault codes?
what about the flashing Red light?
how many times is it flashing quickly? It will pause between message/code of quick blinks.
To assist, more info needed.

Replace your flame sensor

Often, heater problems are not with the heater at all. Make sure the pump and skimmer baskets are clean and backwash or clean the filter.
www.cpo2go.com

Check your connections from the fan to the pressure switch for the fan. It will be a tube comming off the fan housing, follow the hose to the pressure switch. Use a jumper wire on the pre. sw. and see if that helps then check the hose and connections to be sure they are clear. Worst case between 70-80 dollars for the pre. sw. and you can do this yourself. If this does not do the job I suggest another repairman. Good luck.

Sounds like the controller is the problem. This is the circuit board that has the display and controls on it. You can swing that panel open and try tapping on the white plastic cover the controller is under that. This might get the fan relay to release but you will have to replace the controller it will stick again