Sta-Rite Max-e-therm 333k pool heater E-05

[Filtiarne]

I have a Sta-Rite max-e-therm 333k pool heater that wasn't working when I bought my home. I have replaced the blower, the stack flue sensor, the gas valve, the transformer, pressure switch, air flow switch and the membrane. I also took out the igniter and cleaned it. It was pretty much pristine so i put it back without replacing. It didn't turn on at all before but now it starts up, ignites and starts to heat but then shuts off after a minute or less. I already replaced the stack flue sensor but when I hold in the 'pool on' button the temperature reading is still allover the place. Often rapidly switching between 80 and zero. I have a high limit 135°F sensor, Gas Shutoff 140°F sensor, Thermistor replacement and a thermal regulator replacement coming on Monday. Basically replacing every easily accessible and commonly replaced part I could reach without difficulty. I'm hoping these will help solve the issue but from what I've been reading an E-05 error is caused by the stack flue sensor so I'm a little stumped considering I already replaced it. Does anyone else know what could be causing my issues?