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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 desired temp is reach. Sometimes this will occur 3-4 times depending on reaching 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$(!). I ordered one myself and replaced it last weekend. Took me 5 minutes and switch was 60$. 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 are blocked. 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 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 with 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. 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 furnace tells how many feet of vent pipe are 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 up draft 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 furnace when vacuuming out the condensate line will ruin the diaphragm on the pressure switch. 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,

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

  1. 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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