Pentair MasterTemp 400 error code

[petedog85]

My heater stopped working suddenly and won't turn on via phone app or iAquaLink remote. The panel show what I think is an error code, it says Ad0.
I can, however start it manually though. I think it might have something to do with the stack flue sensor!?
Can anyone please help?

 

[JamesW]

I suspect that the membrane pad is probably bad with the "Off" button stuck.