E74 Error Troubleshooting

[bigal6921]

I am at a loss. This occurred over the summer and was remedied by changing the filter (which did not seem to be dirty enough to cause any issues). Now this is occurring again (cycling dozens of times a day in short increments) after changing filters again. I have scoured the internet and have tried all of the remedies, including vacuuming the drain lines and switching the connection from Rh to Rc, to no avail. My furnace (Bryant 912SC) is not equipped with a float switch on either drain line, which most have determined was the fix for their issues. What could possibly be causing this? 

[Markjosephp]

Hello bigal6921,

I'm sorry to hear about the ongoing issues with your furnace cycling frequently, despite changing the filters and attempting various remedies.

The system might not provide enough power or any power to either the thermostat or a specific wire (so the thermostat can’t complete a circuit and shows a report). Given that you've already checked and addressed several potential causes, it might be beneficial if you could share with us the actual power readings on your Nest Thermostat. You can gather them in the Technical Info settings. Also, does it have a C wire? If so, remove it and leave it disconnected, then gather the power readings without it.

Let us know how it goes.

Best regards,
Mark

[bigal6921]

Thanks, Mark. I am happy to report that I was able to further diagnose and remedy the problem. It appears that the filter I was using (4" MERV 13 Pleated from FilterBuy) restricted too much airflow and was causing the furnace to error and shut down for a brief pause then try again, resuming the on/off cycle. I purchased a 1" MERV 8 filter and have not experienced the issue since. 

[Markjosephp]

Hi bigal6921,

That's great news! I'm glad to hear that you were able to identify and resolve the issue with your furnace. It sounds like changing your filter specs made a significant difference by allowing better airflow and preventing issues and shutdown cycles. It's always satisfying when troubleshooting leads to a successful solution. Thanks for updating us on the outcome, and if you have any more insights or experiences to share, feel free to let us know or start a new thread for any future questions or concerns.

Warm regards,
Mark