Hi,
I have a very old (not sure, but could be 30-year old with the house) Bryant furnace (model 518A030). It used to rarely skip a start, but two days ago it just stopped solid with error code 31. Based on Internet information, it seemed that the Pressure Switch (PS) was the most likely root cause, but mine worked just fine (open-close) and the problem turned out to be the Draft Safeguard Switch (DSS), which is serially connected with the PS and was stuck open. I shorted the DSS and the furnace is now working, but could not find much information on its role and replacement.
In one document, it is described as
"Also known as a vent limit switch. They are NC switches usually mountd on the draft hood if the furnace has one. They monitor the draft hood temperature and open when there is any spillage of flue gas."
So I am concerned about potential safety if gas leaks, but the DSS was stuck open even when the furnace was not operational for 2 days, therefore it could not be detecting real gas to stay open. My CO detector is not showing any concern either.
Hope I can get a more definitive response of DSS function and replacement. Thanks!
P.S. Attaching a couple of pictures with the DSS and the shorted (working) configuration.
I have a very old (not sure, but could be 30-year old with the house) Bryant furnace (model 518A030). It used to rarely skip a start, but two days ago it just stopped solid with error code 31. Based on Internet information, it seemed that the Pressure Switch (PS) was the most likely root cause, but mine worked just fine (open-close) and the problem turned out to be the Draft Safeguard Switch (DSS), which is serially connected with the PS and was stuck open. I shorted the DSS and the furnace is now working, but could not find much information on its role and replacement.
In one document, it is described as
"Also known as a vent limit switch. They are NC switches usually mountd on the draft hood if the furnace has one. They monitor the draft hood temperature and open when there is any spillage of flue gas."
So I am concerned about potential safety if gas leaks, but the DSS was stuck open even when the furnace was not operational for 2 days, therefore it could not be detecting real gas to stay open. My CO detector is not showing any concern either.
Hope I can get a more definitive response of DSS function and replacement. Thanks!
P.S. Attaching a couple of pictures with the DSS and the shorted (working) configuration.
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