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garrygoeson, Home Appliance Technician
Category: Pool and Spa
Satisfied Customers: 469
Experience:  Over 27 years Repairing Pool & Spa Equipment,Gas Heaters,& Whirlpool Bath Tubs. Certified by many Pool & Spa Manufacturers.
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I'm having the same problem as above. I have the exact same

Customer Question

Gary- I'm having the same problem as above. I have the exact same pentair master temp 250. I just replaced the stack flu sensor, but same e05 is flashing. Ventilation is fine on all counts. Can u help?
Submitted: 1 year ago.
Category: Pool and Spa
Expert:  garrygoeson replied 1 year ago.

Does the heater fire and run for a few minutes and then display "E05, or does it display the code right away without firing?

Customer: replied 1 year ago.
It fires up for 30 seconds, then stops and the code pops up. The intake is clear and so is the exhaust.
Expert:  garrygoeson replied 1 year ago.

Check all the wiring connections, (especially between the circuit board and the sensor) to be sure they are not corroded and are on tight.

Customer: replied 1 year ago.
Pulled all connectors and replaced. No corrosion. Everything is tight.
Expert:  garrygoeson replied 1 year ago.

Is your heater running on natural gas or propane?

Expert:  garrygoeson replied 1 year ago.

check to be sure there is adequate gas pressure

Customer: replied 1 year ago.
It's natural gas. Pressure is correct
Expert:  garrygoeson replied 1 year ago.

These are the possible causes of a display of EO5:

High exhaust Temperature (Exhaust temp at the internal area of the stack flue sensor must be less than 450 degrees F)

Sooted Heat Exchanger

Calcified Heat Exchanger

Low or improper water flow.

Customer: replied 1 year ago.
I think you left out the fact that it could be the control board, which I'm leaning towards this being the issue.
Expert:  garrygoeson replied 1 year ago.

In my experience, based on your description of the problem, I have never found it to be a problem with the Control Board. I left out the suggestion of it being the Stack Flue Sensor, since you stated you already replaced it with a new one.