Heater wont fire display not reading anything no error codes on IID or lights on back of board

I had same issue yesterday in the field. The sensor was bad in my case. After replacement of the Stack flu sensor my stack temp was only reading 80 degrees, a clear indication that the board needed to be replaced as well.
Replaced board and the heater fired fine and the stack temp reading was normal, 300 degrees.
To obtain a stack temp, after the heater fires hold down the pool or spa button until the temp appears in the display. It will time out after 10-15 seconds.

call for service

All appearances - No fuel to ignite!
evrything else looks good, proper gas pressure, proper volts at igniter, etc - it should ignite! If fuel present, heater should Fire!
make sure all valves are open.
Gas valve is ON
AND purge any air from gas line.
IMPORTANT ****. If you bled gas line, don't try to ignite for a few minutes. Allow gas to dissipate first, use a fan to help.

Let's get more info!
Take off the front panel of the heater... If you have space to kneel down and look under the display to the back of the circuit board then front panel us all you need to remove for now, if it's too difficult to see or if you have no space then the top panel would need to be loosened by removing the wing nuts on each corner. If you do loosen the top panek be careful when lifting it as the wires are still connected!

Turn heater on and tgen check the back of the board to see which tiny red lights are on , take note of which are on and what abbreviation is next to the illuminated light.
this will tell you which area of the heater the issue is then repost with that info

Does it stay fired or does the fan just run for a few minutes after you shut it off?

what is it doing, what is not doing?
What error messages, if any?

I have the same exact problem with this unit. Obviously getting gas to the unit, because it runs and pumps out some serious heat for a short time, but then kicks off. Did anyone ever figure this out or did you buy a new heater? :-)

E05 and E06 is the error codes for a faulty stack flue sensor. try changing the sensor first is the cheapest. if that doesn't work check for corrosion on control board in which case will have to change out board.