[Baboolian]

Hi,

I've got a Bryant 373lav furnace that is giving me error code 31. When it runs, it blows air but does not produce heat.

If I reset the limit switches it will produce heat and function normally for about 5 minutes before reverting back to code 31. I repeated this process while resetting one switch at a time, and found the culprit to be the Blocked Vent Safeguard Tube and Switch (Component #9 on page 3 in the manual).

Does anyone have a suggestion on next steps to further diagnose the problem? Could it be that the limit switch is bad, or is it more likely a legitimate vent blockage?

Thanks!

 

[yuri]

Those switches never go bad.
Check your chimney for blockage.
Where the vent pipe attaches to the furnace remove it and look inside for dead birds. Yours is a reverse/counterflow I believe so that may be hard as it goes thru the furnace cabinet. Birds get gassed and fall in sometimes and I have had them go all the way down to the exhaust/ventor fan.

You may also have a cracked heat exchanger and need a experienced Bryant or Carrier ( same company ) Pro to check it. Could also be overfired.

If you have a negative air pressure in the house caused by a fireplace or running kitchen exhaust fans and a clothes dryer at the same time it can happen.

 

[beenthere]

Home air pressure problem as Yuri said, or a chimney/vent pipe problem.