My 4 year old heater will run for 24 minutes then turn off with an error code of E05.

I can restart and it will last 18 minutes then turn off with same code of E05.

I can restart again and again and the time it will stay on dimishes each time....it will last for 14 minutes then only 10 minutes always getting the E05 code.

2 pool service guys who claim they know this heater well tell me all the parts check out fine...ignition, fan, hoses are clear etc.  

It does have a bad problem with rust and corrusion eventough it is only 4 years old and both pool guys think this must be the problem.

Could the rust and corrusion be causing it to turn off?   

What should i tell my pool service guy to double check?