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State Select Power Vent HWH (AO Smith) short cycle AFTER proper heating

State Select Power Vent HWH (AO Smith) short cycle AFTER proper heating


  #1  
Old 06-04-16, 10:32 AM
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State Select Power Vent HWH (AO Smith) short cycle AFTER proper heating

I am trying to determine the cause of the following symptoms:
When heat is called for, all sequences function correctly: power vent comes on, pressure switch makes, burners light. Everything runs fine and water heats. BUT, after this sequence, and burner & vent shut down, the HWH begins to short cycle.

The error code indicating a pressure switch not closing after 5 seconds flashes briefly, but, the burners light, it runs a few seconds, shuts down, then does it again, and again and again. It will eventually lock out. If I lower the temp (eg: from C to ab) , while it's short cycling, it will stop cycling. If I let it be, it will lock out. Is this some sort of temperature gauge problem? And if so, how to fix?

I have removed and cleaned the burner unit igniter with steel wool, and this helped with my initial problem (I suspect) with the unit short cycling virtually all day long...but even though it will heat the water now, it still obviously has a problem. The intake and exhaust vents appear clear. Originally, before I cleaned the burner unit, I was getting the pressure switch error code and the unit would lockout.

It is an older model, but gently used. state select water heater PR650XBPDTD.
 
  #2  
Old 06-06-16, 12:25 PM
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I cant find the handbook on that unit... Its a state select?

You need a multimeter and test the ignighter. The resistors go bad at the miolex connector where it plugs into the intellivent gas valve...

It can be the fan is getting weak and cant pull in the pressure switch but most times it would not light at all. If it breafly lights then goes out its usually the flame sensor.. But thats part of the whole HSI assembly...

Read here on how to test the ignighter..

Let me know what you find out...

http://www.statewaterheaters.com/lit...320988-000.pdf
 
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Old 06-06-16, 04:24 PM
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Thanks lawrosa, will do as you suggest and re-post when done. And yes, it's a State Select.
 
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Old 06-10-16, 05:58 AM
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Larwosa: ran tests on resistance, continuity, all were OK..the problem was intermittent in that at first the HWH would work, then something was causing the pressure switch to fail, but then it would recover, then fail, then recover. I decided to run a new vacuum hose outside the tank from the switch to the blower/fan motor, since I couldn't be sure for a certainty that something I couldn't see in the old hose wasn't causing a slight blockage...that fixed it enough to run longer, but still fail. Then, I did what should have been the obvious....took the blower/fan apart,and it was kinda dusty, and had a bit of gunkage....cleaned it up...and voila....all seems to be A-OK now. No pressure switch failures/ short cycles. Apparently the P-switch just wasn't getting enough suction to keep it closed. it was borderline. So there were actually 2 problems, the line was probably just kinked enough, inside the tank where it could not be seen, and the motor was just dirty enough, that the system failed. Even though air was passing through the line, and the motor did vent and suck, it just wasn't enough. So far (24 hours) it's working. Thanks for your link, that was extremely helpful. I really need to buy a manometer, to make sure the motor is strong as needed probably, in case the issue returns.
 
 

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