Hi there, how are you doing?

We have a "Bryant Plus 90" which was purchased about 10-13 years ago.
It's been working great until about a year ago we had to "reset" it
and it went back to work. Recently the LED shows a error code (31,
three short blink and then one long blink) which according to the
manual meaning:

PRSSURE, DRAFT SAFGUARD, AUX-LIMIT SWITCH(WHEN USED)OR BLOCKED VENT
SWITCH(WHEN USED) DID NOT CLOSE OR REOPENED (DOWNFLOWONLY)
If open longer than five minutes, inducer shuts off for 15 minutes
before retry.
Check for:

* proper vent sizing
* defective inducer motor
* restricted vent
* excessive wind
* low inducer voltage(115VAC)
* defective blower motor or capacitor
* defective pressure switch
* inadequate combusstion air supply
* disconnected or obstructed pressure tubing

If it opens after trial for ignition period, blower will come on for
90 sec. recycle delay.
--

Just wondering if anyone knows anything about typically for such as
gas heater, if got this type of error code (33), what type of problem
it probably has? We would like to narrow it down so that we could
trouble shoot. Basically other than the LED code, the heater could
still be turned on but we don't know when it will stop working. Thanks!