My furnace was throwing a trouble code. The code was 31 and for my manufacturer (Bryant) and others thats is a pressure switch code. I was able to resolve this code and get my heat back on simply by working through the troubleshooting steps not by changing or replacing parts or removing blockages.

Steps I took to find the problem:

  1. Smelled and felt for gas leaks FIRST
  2. Took off furnace cover and observed blinking-light trouble code, 3 short 1 long, sticker on the cover says thats a pressure switch
  3. Power cycled furnace
  4. Replaced filter
  5. Checked outside vent and intake for blockage, felt good airflow through both
  6. Checked drain hoses and pipes for kinks and blockage, flexible pipes inside furnace were bent around a bit but not kinked
  7. Observed burner through observation window, saw pilot ignite, saw main burner fire up

Through the course of trying to discover the problem the furnace came back on normally. I do not like "it just started working again" fixes, something was wrong and may still be wrong and I want it properly fixed not luckily fixed!

What should I monitor over the next few hours or days to ensure that the problem stays fixed?

Are there any parts I should replace as preventative maintenance for this trouble code?

Any actions I should take as preventative maintenance for this trouble code?

Are there any tests or measurements I can take? Voltages? Pressures in the exhaust/intakes?

1 Answer 1


There are a lot of scenarios that can cause a pressure switch to report an error. As an example, one that I have seen that is actually "self-healing", I have seen really cold days where there are ice crystals in the air and as the air is pulled into the air intake it can create an 'ice dam' and thus restrict the air flow enough that the pressure switch does not close. This can melt if the outside temp gets warm enough and it can also be dislodged simply by shaking the intake pipe. I have also seen birds nests and various debris block the air flow. One time I am pretty sure that the wind was strong enough and blowing in just the right direction that it was preventing the switch form staying closed. (I made this assumption because of the homeowners description of his trying to fix it and their location at the mouth of a canyon and the strong winds we had had. You mentioned power cycling the unit. That would reset the error and allow for it to try to come on again. If it is running again it should be good the switch is open and will not run unless all is well.

As far as preventative maintenance, you have done most of what can be. I have seen a pressure switch that had water in it because one of the hoses was kinked. But there is not much else that can be done.

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