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Old 11-18-2012, 09:27 AM   #1
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Lennox SLP98 pressure switch issues


Hi -

We have a two-year old SLP98 furnace that will not light. I have had HVAC techs out three days in a row (at $160/visit) and still they really don't know what is wrong with our furnace. Each time they come out, they try a bunch of different things (mostly the same things the other guy tried), read the error codes and after a bunch of trial and error, the furnace lights again and we have heat for approximately 12 hours.

After the furnace stops lighting, it keeps trying to calibrate when heat is called for by the thermostat. The inducer comes on and then the pressure switch clicks, then it keeps ramping up, the pressure switch(es) click a few more times, it keeps ramping up and then shuts down, giving error code 228.

All of the venting has been checked and is clear, all of the hoses leading into the pressure switch have been blown out and are clear. All the wiring is intact.

Seems like the furnace just happens to come back on once in a hundred or more tries by the service tech. Once they get it on, they leave and tell us to call again if it goes off. The latest senior service tech said he thought the pressure switch might be bad, so we are waiting for them to order us a new switch. Of course, they can't get one on the weekend.

Anyone else had this problem? The service tech said he thought that he remembered something about the pressure switches for this unit having a problem. Has there been a recall of them?

Thanks for all replies.

Becky Snider

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mississippidave (12-25-2014)
Old 11-18-2012, 09:40 AM   #2
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Lennox SLP98 pressure switch issues


There have been a few failures of those switches but no more than average. The inducer needs to ramp DOWN to its lowest speed to calibrate the high and low aspects of the switch/venting. If it does not ramp down then it usually is the switch AND it is the dual pkg of switches unless you got the latest series which does not have a 3rd pressure switch. Have not had any problems with the latest version of it. THey also should be clearing the error codes off the board B4 they leave.

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Old 01-24-2013, 10:56 AM   #3
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Lennox SLP98 pressure switch issues


I am having the same problem with my SLP98. I was able to get it fired up last night for about 3 hours, but the unit was off again this morning. There is no drainage issue and the vents are clear. The manual says to check the wiring for the pressure switch after clearing the vents. Is there anything else I can do before a tech arrives to eliminate everything besides a bad pressure switch?
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Old 03-18-2013, 02:49 PM   #4
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Lennox SLP98 pressure switch issues


My slp98 behaves in a similar way: upon heat request the inducer spins up, and I can hear a click in the pressure switch. Then it spins for may be 20 sec, and slows down. When it slows down I can hear another click in the pressure switch. Then it stops and nothing happens. What can I do to fix this? The furnace is 14 months old. The furnace shows E228 error code on the thermostat.

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mississippidave (12-25-2014)
Old 03-18-2013, 05:15 PM   #5
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Lennox SLP98 pressure switch issues


call the installer or a certified Lennox dealer. parts should have a 10 yr warranty and there is nothing you can DIY with that furnace except check the vent pipes outside for blockage.
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Old 03-21-2013, 12:45 AM   #6
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Lennox SLP98 pressure switch issues


Sounds like a bad pressure switch, they are finnicky things. Wouldve been two weeks ago now we installed a new carrier 60k btu furnace in a place ans the next day got a call saying it wont light. Was the pressure switch. Im surprised it took two different guys to figure it out though
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Old 12-25-2014, 10:25 PM   #7
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Lennox SLP98 pressure switch issues


I've had the had the same problem with my Lennox SLP98, but I have found something that worked for mine (which was installed in Nov. of 2011.

But first, the setting. Just after midnight on Christmas morning 2014 I was still up wrapping presents when I notice the air temp was cooler - checked the furnace and E228 flashing. Began the on and off every 10 minutes or so. Every Calibration cycle ended with E228. It was Christmas and a big snowstorm was on the way. No way I'm getting a serviceman on Christmas Day. So, I'm left to my own witts, and its either try the witts or have a cold family.

After checking to be sure there were no obstruction in the exhaust or intake or drainage (both ends of each and ShopVac-ing the pipes and tubes to be sure), I commenced my last ditch effort. I turned the furnace off, waited five minutes, turned it back on and waited for the CAL light on the control board (calibration cycle) to start. As soon as it started I began tapping the pressure switch very quickly with two screw drivers, one in each hand (I was a drummer in high school and have a drum set) and maintained the tapping throughout the calibration cycle....and Voila! The flame came on and the heat has been running nicely for 5 hours now.

I know, however, that I will need to put in a new pressure switch, because this will happen again. A least I have a little time now to shop for a good price. I looked at the schematics/drawing and looked over the switch carefully. It doesn't look difficult at all to change. But if I change it, the 10 year limited warranty might be nullified if it is not already from the tapping. For today, I am warm on Christmas, and this advice is my gift to y'all. Hopefully, it will help a future reader to stay warm too.
MERRY CHIRSTMAS Y'ALL!
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Old 12-25-2014, 10:27 PM   #8
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Lennox SLP98 pressure switch issues


Please forgive the typos in previous - I recently dislocated and broke my finger OUCH!
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Old 12-25-2014, 10:34 PM   #9
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Lennox SLP98 pressure switch issues


Oh, and thanks to you all for posting about this issue. Your generosity in taking the time to do so is greatly appreciated and is very helpful to many people. Thank you!
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Old Yesterday, 12:11 AM   #10
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Lennox SLP98 pressure switch issues


Yur Welcome. They won`t know you tapped it. May be cheaper to just buy the pressure switch from cozyparts.com than pay for a service call and labor for a dealer to change it. Make sure you have the COMPLETE model and serial number as there is a series number built in and they need it.

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