Question about Hayward H-series Electronic Gas Pool Heater H400

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I have an ao code and have replaced the vaccum switch and blower vaccum switch and still getting the ao code

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Check the tubing going from the blower to the blower vacuum switch. If there are any cracks, missing, or cut, it will give the same code. Rodents like to chew on this tube. Also, if the blower is not coming on at all, then you will get the same code, and the problem is not with the switch, it is likely in the blower.

Posted on May 22, 2010


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Ao error message in Hayward heaters

You didn't indicate exatctly which model you have. But on most the AO error code is :Blower vacuum switch
open error If the blower prover switch does not close after the blower starts the control will
stop the ignition trial go into lockout. The blower will continue to run. Automatic reset is immediate after the switch closes.Check to be sure combustion blower starts
If you don't have your manual you can download one for your exact model at :

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Your problem then would be the pick up tubing and/or switch attached to the blower that closes once the blower is on to allow the heater to ignite. Pull the tubing and check it for dust or other debris clogging it and check inside the blower housing for the same. If you can test the switch under operation, you should see it remains open during start up which is why the burners won’t fire. If you do not find any obstruction (if you can, blow some compressed air thru too just to be sure) then you will need to replace the switch.

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I would have to agree with you concerning the control module.

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if blower comes on it is calling for heat. i would look at could also be vacuum switch(tube goes to it from blower)however they rarely fail.let me know

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Error code AO defined as blower vaccum open

I just had same code. I took off top cover and found the end of the hose attached to the blower was split and not attached securely. Attaching hose solved the problem for me and heater fired up.

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