Pressure switch error after a long cycle

Pieter Poel

2 years ago

Hello, first time user here so apologies if I'm doing anything wrong and also for the long post...

We have a 9 year old Lennox high efficiency gas furnace, model EL195UHE070...

https://www.manualslib.com/products/Lennox-El195uh070xe36b-9924310.html

Usually it works very well, but sometimes it will fail to start up with a pressure switch error. The motor will start up, run for a couple of minutes and error out without lighting the burner.

We had our serviced twice late last year by different companies and neither could find anything really wrong with it other than a bit of dirt and some relatively long ducting to the exhaust/intake point (though still within the maximum). Both times it was working when they left.

After a few more months of it working *most* of the time, we figured out that it seems to most commonly fail on the cycle *after* it runs for a long time (eg our thermostat was programmed to increase from 18C overnight to 21C in the morning). We've set the thermostat to a consistent 20C now which seems to help but we still get errors sometimes.

The "time after a long cycle" issue has me thinking that it is some sort of condensation drainage issue. The drain connects to a little u-drain type thing on the side (3rd photo) which has been cleaned and looks all ok. Sometimes if I drain out the u-drain it seems to then work but that seems counterintuitive (why would that help?) and maybe just a coincidence.

The only other thing the technician did that I felt comfortable doing myself was disconnecting and checking several small rubber tubes for blockages. In doing so I discovered something else... Disconnecting and reconnecting the small orange rubber tube going from the gas valve to the burner box (not the main gas feed) seems to successfully reset the system. This is top of 2nd photo and circled in blue in 1st photo.

Finally, sometimes the burner will do it's initial ignition (small orange flame) and then extinguishes itself with a kind of huffing sound instead of lighting up fully (blue flame) for proper heating.

Any ideas on what could be the main issue here? Thanks in advance!!

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Comments (4)

Andrew
2 years ago
last modified: 2 years ago
Hi. I soulds liike your furnace is radomly failing at different points within the sequence which could make it hard to diagnose without someone actually being there with the proper tools and knowledge to diagnose. If you were having same issue consistantly, and know the sequence of operations, it would be quite easy to pinpoint your problem. Furnace control boards do flash error codes, but in some cases these codes are ”generic” and do not indentify the excact issue.

You’re furnace is 8 years old, and if it has been properly taken care of, could last you quite some time. If you continue to run it with these random failures, chances are you are your furnace is going to end up failing on you completely and may end up causing damage.

My recommendation would be to have an HVAC company come out and take a look at it while it goes through its’ cycle. Some issues can only be found and repaired with specialized tools. Also, getting a maintenance done on it would be a good idea. (Checking gas pressures, clearing condensate lines, checking components are within proper voltage, amps, ohms, etc, cleaning burners, making sure flue has no blockages, proper airflow, etc). I know you said you had a few companies come out and found nothing, but there is obviously something going on, and since your problems are random, it’s going to be difficult for anyone to help with any accuracy via a forum.
mike_home
2 years ago
sometimes the burner will do it's initial ignition (small orange flame) and then extinguishes itself with a kind of huffing sound instead of lighting up fully (blue flame) for proper heating.

I noticed the gas line is connected copper tubing. This is not good if the furnace is using natural gas. The gas line should the same black pipe as the elbow in the picture. The pipe should have a drip leg to catch any debris. The fact the burner is having problems could be a sign of debris getting into the gas valve orifice. You should have a licensed plumber fix this and the piping to the hot water heater.

Have you inspected the exhaust flue for blockages? Did any of the techs suggest replacing the pressure switch? The condensation theory is plausible. But if it were a condensation drainage problem then I would think it would happen even with short heating cycles and more frequently.

The only way to solve intermittent problems is to be able to reproduce them when the HVAC tech is present. If you can figure out hot to make the furnace reliably fail then you have a chance of solving the problem.
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Pieter Poel
Original Author
2 years ago
Thanks for the response. All the electrics and gas pressures were all fine when checked by the previous technicians. No apparent blockages in air flow or condensate lines that could be found.

The error code is listed in the manual as "Pressure Switch Failed to Close or Opened on Heat Demand". So pretty vague. There's lots of things that can cause a pressure switch to fail to operate properly.

Next thing to try is a new pressure switch I suppose. But I can't shake the feeling that the pressure switch isn't the problem since sometimes it works just fine.
Andrew
2 years ago
It’s possible that the pressure switch could be failing, but in the long run you may be just be replacing parts that don’t need to be replaced. It is possible to bypass the pressure switch and see if the furnace operates normally but that is not a task that should be performed by the average homeowner without knowledge of the furnace or electricity. I would refer back to my previous recommendation to have an HVAC company perform troubleshooting/maintenence on your furncace and do not let them leave without cycling heat several times. If it fails after that, document and call the company back. Make sure to get a breakdown of any and all work done.

Pressure switch error after a long cycle

Comments (4)

Andrew

mike_home

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Pressure switch error after a long cycle

Comments (4)

Andrew

mike_home

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Pieter PoelOriginal Author

Andrew

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Pieter Poel
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