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ComfortZone, HVAC Technician
Category: HVAC
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Experience:  10 years in the HVAC industry.
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Our Trane XR-90 furnace is flashing 3 - pressure error. Of

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Our Trane XR-90 furnace is flashing 3 - pressure error. Of course it is Friday night and it is snowing... Is this something we can fix on our own?

Have you checked the vent pipe outside to make sure it is not covered in snow?


Take the rubber hose lose from the inducer fan. That is the little fan with the rubber hoses coming out of it. See if water comes out of the fan housing.


Something is keeping the pressure switch from closing, which means it is a vent problem or inducer problem.

Customer: replied 7 years ago.
yes, there is water coming out of the hose from the inducer fan.
Is it draining freely?
Customer: replied 7 years ago.

The vent pipe is clear of snow. There is water dripping out of the vent pipe at a joint that appears to have come apart under the house. We put it back together. There is water in the clear tubes that are connected to the inducer fan. There is some water dripping in the lower chamber of the unit, too.



Take the tube from the lower port and let all the water drain from the inducer housing.

Let me know if it was a substantial amount.


Those tubes should drain into a cup on the side of the furnace. Is that cup full of water?


Be sure to put a rag under it to soak up all the water.



Customer: replied 7 years ago.
thank you - this is helpful (our babies thank you, too!). stupid question - how do you get the tube off? just pull? they have black clips on them.
Customer: replied 7 years ago.
nevermind - got it off and no water coming out afterall. we can't seem to tell if the cup is full of water.

Yeah, those clips pinch together with a pair of pliers.


Put the hose back then.


This furnace has 2 vent pipes coming out of the top. They are both made of PVC and are approx 3" in diameter. The pipe that was under the house was probably not the vent pipe, but the condensate drain also made of PVC but only 3/4" in diameter.


Is this a correct assessment?


There is a pressure switch that has a hose connected to it that runs into that inducer housing. Take it loose and make sure it is not clogged at all.

Customer: replied 7 years ago.

The 3" PVC pipe that goes up from the furnace and then out of the house was leaking just about a foot from the furnace. It is reconnected and not leaking anymore.


We found a 3/4" pipe on the left side of the furnace leading to a white box that says "pump" sitting on the floor. We removed the flexible tubing that also led to the white pump and it was full of water.


Upon further investigation, the cup you mentioned before does seem to have water in it - up to the level where the hose attaches on the side (we couldnt' figure out how to get into it before).


We're not sure where the pressure switch is.


Customer: replied 7 years ago.
we just turned the furnace back on while we were waiting. seems to be running again. fan is going. error light is off (or constantly flashing like it's supposed to). is there something we should watch for now (since we don't know what we did that fixed it...)?

Here are some pressure switches. Trace the clear tubes from that inducer, one should lead to the pressure switch.




That pump on the floor is a condensate pump and should eject the water outside.

It has a float switch inside of it that closes when the float gets near the top and that turns on that pump.


Have you tried to start the furnace since you fixed the pipe?

It was probably the loose pipe that was the problem.
ComfortZone and other HVAC Specialists are ready to help you
Customer: replied 7 years ago.
alright! Well, we'll try that. THANK YOU SO MUCH.

Glad to help.


If the problem resurfaces, do not open another question. Post back to this one. I think you have solved your problem though. Stay toasty...............