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Problem: Furnace blink code shows I have a pressure switch problem. Replaced pressure switch. Still have a problem?

Problem: Hello, love the website and help that it offers. But I seem to be out of options with my furnace here. I have a Carrier HE furnace that is not even 3 years old yet. We have had repeated issues with the furnace running for 2-3 minutes, stopping, recycling, and coming back on until the desired temp is reached. Sometimes this will occur 3-4 times depending on reaching the desired temp in the home. When I called a technician he came out and charged 170$ just to tell me my pressure switch was broken. And offered to replace it for another 150$(!). I ordered one myself and replaced it last weekend. Took me 5 minutes and the switch was 60$. But, I’m still having the same symptoms. Sometimes the furnace will not even come on and we awake to a cold house. Other times it works just fine…??… it’s “buggy” as I describe it. I am getting a 3 to 1 LED code indicating pressure problems. But I have cleaned the water trap multiple times and there seems to be no issue. No water lines to or from being blocked. The exhaust is not blocked leading outside. Nor is intake. And again the pressure switch is brand new (supposedly). And I have also cleaned the flame sensor with a newspaper (no steel wool). I don’t believe that is the problem. Seems clean. No residue on it. So, if you can offer any help please do! Cleveland is about to have sub-zero Temps coming up this weekend! Chris

Answer:  Hi! I am terribly sorry that you have encountered all these problems with your furnace. We have a furnace troubleshooting flow chart that I hope will help you out on the following page: Please click here if you would like to see our Gas Furnace Troubleshooting Flow Chart. I would start by making sure the thermostat is providing 24 volts between W and C terminals on the control board when the furnace cuts off. If you are getting a constant 24 to 28 volts AC to the furnace all the time between W and C when the furnace cuts off then this would eliminate the thermostat from being the problem. If the control board is correct in saying and showing that the pressure switch is the problem… then I would suggest looking at the things like you have already have, like the condensate trap and drain lines from the secondary heat exchanger. We have a really good YouTube Video made by AC Service Tech, below that shows how to properly clean out a furnace’s condensate drain lines and trap. Please make sure the furnace is tilting forward slightly so the water drains out the front of the furnace. The installation instructions on these high-efficiency furnaces tell how many feet of the vent pipe is allowed for venting. If the allowed vent feet are exceeded then you will have trouble with the pressure switch not staying closed. The 90 degree turns in the venting sometimes are calculated as 5 feet of piping. If you have exceeded the number of turns the furnace will not run right and the pressure switch will not work or stay closed. I remember one furnace I installed where I tried to use 2″ PVC for the venting and ended up having trouble with the pressure switch going off like your furnace is doing. I ended up having to tear the 2″ pipe out and install 3″ PVC vent. The venting is critical for these high-efficiency furnaces to run right, to say the least! Some other things that cause furnace pressure switch problems are: (1) A restricted vent pipe (2) Too long of vent piping and too many turns which exceeds manufacturer’s recommendations (3) a stopped-up condensate drain line if you have a high efficiency condensing furnace. (4) a dirty or stopped updraft inducer. The hole where the pressure switch attaches to the draft inducer could be stopped up with water, slug, or dirty. (5) a slow draft inducer that might need a new capacitor or has slowed down. (6) someone has sucked on the pressure switch with their mouth or forgot to unhook the pressure switch from the furnace before using a vac on the furnace. Sucking on the pressure switch or leaving a pressure switch attached to the furnace when vacuuming out the condensate line will ruin the diaphragm on the pressure switch. (7) A leaking heat exchanger. If your furnace has a leak in the heat exchanger combustion gas is allowed to mix with air in your home or in with the blower motor air. This hole in the heat exchanger will not allow the negative pressure that the pressure switch needs to close and operate properly. If you find that you have a hole in the heat exchanger then you need to replace the heat exchanger or get a new furnace because this creates a dangerous condition that can allow carbon monoxide into your home.  I hope you can find and fix the problem. If you need parts please send me your furnace’s product number. Please email us anytime if you have a question. Our email address is If you think you have a bad pressure switch Please click here to see the furnace pressure switches we sell. I hope you have a blessed day.  Steve Arnold

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14 thoughts on “Problem: Furnace blink code shows I have a pressure switch problem. Replaced pressure switch. Still have a problem?

  1. I keep getting the 3 blink light code on my Goodman 36100. The code says it’s a pressure switch.
    If i unplug one of the wires from the limit switch, everything starts working great. Then i plug the limit switch back in and it will run normal for days, sometimes weeks before it does it again. Is it the limit switch going bad or something to do with the pressure switch?

    1. Hi Chris! The only way to tell where the problem would be to test the limit and pressure switch with a voltmeter the next time the problem occurs. We have a troubleshooting pressure switch page that I hope will help: We have another post that I hope will help on the following page: We have some good Youtube videos too. Since we can not see electricity using a voltmeter is important for troubleshooting problems. I hope you can easily find and fix the problem. Steve

  2. Hi Steve,
    I have an Aire-flo furnace 92AF. I replaced one of my pressure switches, the one connected to inducer motor, then the furnace fired up. After worked sometimes 3 mins, sometimes 10 mins, the inducer motor shut off always. Rollout and limit switches are good (I jumped to test them), cleaned all I can. Any ideas for my issue please? It looks like only inducer motor and control board left….

    1. Hi Barney! Yes, It sounds like you either have a draft inducer problem or a control board problem. I would like to suggest that the next time the draft inducer shuts off during the middle of a cycle to make sure you are getting low voltage (24 to 28 volts AC) from the thermostat between the W and C (com) wires. If you are not getting 24 to 28 volts between W and C then you would have a thermostat or a thermostat wire problem. If your thermostat uses batteries then make sure the batteries are in good condition. If you are getting 24 volts between W and C then I would suggest testing the voltage coming out of the control which goes to the draft inducer. Test with a voltmeter set again to “Volts AC” and see if the draft inducer is getting between 110 to 125 volts. If the inducer is not getting 120 volts then you have control board problem. If the inducer is getting 120 volts and not running then you have a draft inducer problem. If your draft inducer has a capacitor make sure the capacitor is in good condition. I am sorry, but I do not have an Aire-Flo furnace parts program where I can look up parts. I hope you can easily find and fix the problem. Steve

      1. Thanks Steve!
        New batteries for the thermostat. Tested inducer motor capacitor with a meter, all good.
        The inducer motor starts, the ignitor glows, gas goes out from the the valve, fires up, blower works, then a few mins later, the inducer motor shuts off, the red light blinks 3 times, which means open pressure switch….

      2. Hi Barney! Yes, if the draft inducer goes off in the middle of the heating cycle then you will get the “Open Pressure Switch” fault. I would suggest that you do the testing that I described in the earlier post with a volt-meter to determine if you need a new control board or a new draft inducer. Without testing with a meter it is a guess. I hope you get it fixed soon! God bless you. Steve

  3. Hi, I have York furnace. My furnace is working fine in the last few years and it just having issues now. Thermostat calls for heat, inducer motor starts but not ignite and after 30 seconds I can smell gas. and after few minutes the inducer motor shut down and led light flashing 7 times. I swap out igniter, flame sensor, pressure switch and check high limit switch still good (normally closed) . Do you think I have issue with control board? Please advise. How do I check to find out the control board is the problem? Thanks for any help.

    1. Hi Dan! If all your safety controls are closed as you said and your hot surface ignitor is not glowing then it has to either be a control board problem or an ignitor problem. We have a good post with two YouTube videos on the following page: I would like to suggest that you test to make sure that the ignitor is getting 120 volts AC during the ignitor glow phase of the ignition cycle. If the ignitor is not getting 120 volts AC when it is supposed to be glowing then it is a control board problem. It would be best if you could test the voltage with the ignitor load hooked up in the circuit. Sometimes controls boards with show 120 volt when the ignitor is not hooked up, but when the ignitor is hooked up the voltage will go to zero or really low. You should be able to light your furnace manually if your family is really cold. Here is a link to that page if you want to try and light your furnace manually. I hope you can easily find and fix the problem. Steve

      1. Thank you Steve,

        I checked and no 120v go into the ignitor. I ordered a control board from your website already. Thanks for your help.

      2. Hi Dan! Thank you so very much for your business! If all your safety controls are closed like the pressure switch, limit, rollouts and if you are not getting 120 volts to the ignitor then it almost has to be a control board problem. Just make sure that you have 120 volts coming into the control board between L1 and a neutral (white wire). I am shipping your control board out today. I hope that it fixes the problem. Thanks so much for your business!!! Steve

  4. Hello I have a Heil mid efficient furnace. With a smart gas valve that flashes code 3 (low pressure switch stuck open) I have replaced the switches cleaned the furnace and inducer motor is spotless. Clean and I still get the same code what could be the problem the furnace is. 14 years old and I have never ever had any problems until now any recommendations ?

    1. Hi Mr. Rankin! Sorry to hear that you are having problems with your furnace. I would like to suggest that you use a voltmeter to see if the pressure is actually stuck open. You would need to turn the thermostat up so that the heat is on and the draft inducer is on. The low-pressure switch should close and provide 24 volts AC between each of the two terminals on the pressure switch to a good ground. If the pressure switch will not close as the board is flashing then you have found the problem. Here is a link to our pressure switch troubleshooting page: If the pressure switch is closed then you must have another problem that is causing the furnace not to work. I would recommend that you check and test all safety controls like the limit and rollout switches to make sure they are all closed. If these safety controls are all closed then I would think that you either have a furnace control board problem or a Honeywell Smart valve problem. We have a troubleshooting Honeywell Smart Valve page that I hope will help: I have seen these Smart Gas valves cause lots of problems. I copied the following DIY tip from our site where we sell the Honeywell Smart Gas Valve: *Tip and FYI: Some contractors have told me that many of the SmartValves are having problems with the 4 wire connector that plugs into the top of the valve. If you can hold the 4 wire connector in the right place many times the valve will work. Some contractors have told me you can use a matchstick to hold the 4 wire connector in the right place so the valve will work. I hope you can easily find and fix the problem. Steve

  5. I have a Goodman furnace with dual pressure switches. GMS90453BXA MODEL NUMBER. Replaced both pressure switches . Furnace come on but will not start when call for heat later. I was going to order an inducer motor.

    1. Hi Ms. Jackson! If the inducer motor will not come on it could be the thermostat not allowing the furnace to start. Please make sure you are getting 24 to 28 volts AC between the W and C (common) terminals from the thermostat when you have the thermostat calling for heat. If your thermostat uses batteries please make sure they are in good shape. Also make sure the control board is sending 120 volts to the draft inducer when the thermostat is calling for heat. If the control board is not sending 120 volts to the inducer then you might have a control board problem. Please make sure you are getting 120 volts to the control board by testing between L1 and one of the neutral terminals. Please make sure the fuse is not blown on the control board. The control board your furnace uses is a PCBBF112S like we sell on the following page: The inducer part number is a 22307501S which has been updated to part number 0171M00000S. We sell this inducer on the following page: I hope you can easily find and fix the problem. Steve

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