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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I own an AO GDHE 50 natural gas hot water heater. A while

Customer Question

I own an AO Smith GDHE 50 natural gas hot water heater.A while ago, I would periodically see a "Blocked Exhaust" error, perhaps every few weeks, that could be reset by turning the power on and off.I looked down the vent exhaust using a fiber optic and did not see any obvious obstruction, so when it happened periodically, I would just ccle the power and the issue would disappear for several weeks.Lately, the error frequency has gone up, to perhaps every few days. It's also most likely to occur when running several kids showers in a row. Recently, when the system trips and displays a "Blocked Exhaust" Error, I noticed that the error message suggest checking if the condensate is draining. As the condensate pump was coincidentally full when the errors occurred, and was sounding a bit "tired" I replaced it.The problem has not been eliminated with a new condensate pump.I did scroll through the error to see the "advanced info" and found:Error: Blocked Outlet
Error Code: A8
Error Data: 0x50Possible causes:1) Blocked condensate drain (on exhaust elbow)
2) Restricted exhaust vent
3) Excessive equivalent pipe length (too long or too many elbows)
4) Loose or open wiring connections to blocked exhaust
5) Blocked exhaust pressure switch out of calibration (replace blocked exhaust pressure switch)I can check #1 and #4, I can recheck #2, and #3 is highly unlikely as this is not a new install (>6yrs in service).What is the likelihood of it being #5, and how would I test that, or would one typically just replace it?How would you approach troubleshooting/solving this? Thoughts?Thanks in advance,John
Submitted: 9 months ago.
Category: HVAC
Expert:  D.E. Anderson replied 9 months ago.

Hi, how are you? I would disconnect the wiring running to the switch and run the water heater through its normal start up sequence, I would take a ohm meter and ohm out the pressure switch during the start up while the exhaust motor is running. If the switch closes, then the switch is good. If the switch remains open, then either the flue is blocked or the switch is defective. I would say most likely you are looking at a defective switch. Also, check any tubing running to the switch for clogs as well as clogs at their connectors. If you have further questions please feel free to ask. Thanks