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My American Standard furnace ("Standard" Model, year 2003, 12 or 13 SEER) gave an Error Code 2 when first turned on- "External lockout, retries or recycles exceeded." (4 fail to ignite cycles observed.) I turned off the switch for maybe 30 seconds and turned it back on. It ignited in the second cycle, heated the house, and shut off. When it came back on later, it was not blowing hot air. No flame, Error Code 3- "Pressure Switch Error." This has happened several times.

The pressure switch reads open at rest. If I use a straw to suck on the tube, there is a reading of about 3.9, trending down to about 3.2 before I have to stop to exhale. I think this rules out a bad switch. The inducer motor runs, and the fins on its fan appear to be clean. There don't seem to be any obstructions in the air flow, but I can't take the vent sections apart, as they are snapped firmly together. I went up on the roof, and the vent was clear. If I turn on the furnace and let it run without igniting, should I be able to feel a definite air flow when I go back up on the roof, or a suction on the tube from the inducer motor? And is it a bad idea to jump the 2 pressure switch wires to mimic a closed circuit? I want to rule out everything else before I try to replace the circuit board.

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  • Can you post the model number for your furnace?
    – ThreePhaseEel
    Commented Nov 7, 2019 at 3:21
  • Error code 3 is unique to whatever furnace controls happen to be in that furnace; so far as I know there's no industry standard to them. Look on the inside of the blower or burner door for a label that gives a description for code 3 and edit that into the question.
    – Greg Hill
    Commented Nov 7, 2019 at 15:59
  • We need an actual model number from the furnace's nameplate -- if you could post the wiring diagram for your furance, that'd help too
    – ThreePhaseEel
    Commented Nov 8, 2019 at 1:06
  • I can't find anything identifiable as a Model Number- Do you know what kind of alphanumeric designation I should be looking for?
    – Joseph Filip
    Commented Nov 8, 2019 at 1:46
  • Photos of all the labels inside the furnace would do. :-) There's generally a large label on the inside of the blower door and one or more smaller labels inside the burner compartment -- these are often on the side wall and not immediately noticeable.
    – Greg Hill
    Commented Nov 8, 2019 at 5:25

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Yes it sounds like the pressure switch may be working correctly. If you'll be in constant attendance and feel confident about your ability to detect any problems, you could use a jumper in place of the pressure switch. You'll likely find that the controller verifies that the switch is open when the inducer is off and closes when the inducer is on -- so the jumper will have to be placed and removed at the right times.

The fact that the furnace sometimes ignites but other times not, and that sometimes the air blower remains on, suggests to me a problem with the flame proving function. Maybe have a look at After blowing heat the fan won't stop, continue blowing cold air for prolonged period of time (30+ min). Power cycle the furnace and observe its operation through several run attempts as described there.

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  • I will check out the suggestions in the link. I did get an Error Code 8- "Low flame sense signal" about 3 years ago. I removed the igniter, which looked fine until I was ready to put it back in place- one of the "tines" had broken off, probably by me when I set it down. Can the fragile "tine" type igniter be replaced by a sturdier-looking rod type?
    – Joseph Filip
    Commented Nov 8, 2019 at 0:27
  • Sorry, I'm not familiar with the electrical specs of igniters to be able to say whether one form factor could be replaced by another (physical/mounting considerations aside).
    – Greg Hill
    Commented Nov 8, 2019 at 5:28
  • Before asking my question, I had examined and fiddled around with a couple of dozen possibilities. It still wasn't working, but now suddenly it is, and I haven't actually changed anything since it was NOT working while I was going through your suggestions. So I'm going to wait until it fails again and then carry on with your very helpful hints.
    – Joseph Filip
    Commented Nov 8, 2019 at 19:24

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