How do you remove the top cover to replace the blower on minimax nt heater?

check the air flow switch the fan must close this switch for the ignitor to light

Go to Grainger or a Heating & Air Conditioning
Supply House or Wholesaler

Take the part with you

On a Pentair, this means Lockout.
its a safety precaution that disables the heater. To unlock, simply power cycle heater off and then back on.
If this continues, diagnostics required to identify reason for non ignition.
Does Service light come on?
if so, you can either remove the front panel and look up behind the circuitboard, or actually the backside of the control panel circuit board. or remove the top of the heater, there are four wingnut each corner on the bottom side of that top cover. your goal is to clearly see the backside of that touchpad. There will be a red light and you want to see the letters next to it. this will be the indicator of the problematic situation.
Report back any findings in the comment section or in a new question on this forum.

Hope you are using lots of insulation. I have a bubble cover exposed during sunny days then put pool cover over at nite. Also have 4 x 8 ft Styrofoam pink insulation on top of the bubble cover. That costs $19 per sheet at Home Depot. 2" thick R 10.

Check the limit switch. It may be stuck open. TAP the cover with a screwdriver. If the unit starts, the limit will be the problem. You should also check the flame sensor. The unit may try to start but the flame sensor doesn't see the flame, the unit shuts off..Good luck...Lee

replace valve assembly

ign failure code, replace ignitor

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