Code AO is on display. Went throught the

The most common reasons an INFINITI I35 heater isn't working are a broken heater blower motor, a problem with the thermostat, or a failed heater blower motor resistor.

INFINITI I35 Heater Is Not Working - RepairPal.com

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The brown wire at the speed switch is the power wire. Powers is then directed to the blower motor resistor throught the orange, lt blue and yellows wires. The blower motor receives power through the orange wire. Check for power at the fuse with the key on. If there is no power the problem could be the ignition switch or the wiring in between the switch and the fuse block

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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 : www.haywardnet.com

AO will apply to your blower, blower tubing, or blower vacuum switch. You need to check these items.

You need to check and see if you have enough gas supply to run the heater. Older heaters would run on a small gas supply but forced draft are hinkey about how much gas they get. Sometimes this is a gas line size problem but more often than not it will be a gas meter problem. On the face plate of your meter their is a number that tells the size. With a 250 and other appliences in the house you will want a 350 or bigger. The good news is the gas company will upsize this for nothing. If they are supplying more gas your buying more gas. It could be other things but this is the first thing to look into.

The AO mindicates an open prover switch ,, here from Hawward site .
If the blower prover switch opens unexpectedly during operation the control will
shut down and attempt to re-light. If the switch does not close after the blower
starts the control will go into lockout with the blower running. Automatic reset is
immediate after error is corrected.

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 your wiring again on all the safety devices - Water pressure switch and both Hi- limits in the header.

Thank you for posting your question here on Fixya.com.

It sounds as if the air activated switch the tube you mention attaches to is not working. Pull the two wires from it and connect them to simulate the switch closing. Start up the heater to see if you get ignition. If so, replace the switch.

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John

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.

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